diff --git a/core/assocs/assocs-docs.factor b/core/assocs/assocs-docs.factor
index 6170eddf52..68be9c9b06 100755
--- a/core/assocs/assocs-docs.factor
+++ b/core/assocs/assocs-docs.factor
@@ -1,7 +1,7 @@
 ! Copyright (C) 2007 Daniel Ehrenberg and Slava Pestov
 ! See http://factorcode.org/license.txt for BSD license.
 USING: help.markup help.syntax kernel sequences
-sequences.private namespaces classes math ;
+sequences.private namespaces math ;
 IN: assocs
 
 ARTICLE: "alists" "Association lists"
diff --git a/core/bootstrap/image/image.factor b/core/bootstrap/image/image.factor
index 2f354bfee5..cb73dc387e 100755
--- a/core/bootstrap/image/image.factor
+++ b/core/bootstrap/image/image.factor
@@ -404,8 +404,8 @@ M: quotation '
     [
         {
             dictionary source-files builtins
-            update-map class<-cache class-not-cache
-            classes-intersect-cache class-and-cache
+            update-map class<=-cache class<=>-cache
+            class-not-cache classes-intersect-cache class-and-cache
             class-or-cache
         } [ dup get swap bootstrap-word set ] each
     ] H{ } make-assoc
diff --git a/core/bootstrap/stage2.factor b/core/bootstrap/stage2.factor
index 8e4108866f..3247832d52 100755
--- a/core/bootstrap/stage2.factor
+++ b/core/bootstrap/stage2.factor
@@ -44,10 +44,6 @@ SYMBOL: bootstrap-time
     "Now, you can run Factor:" print
     vm write " -i=" write "output-image" get print flush ;
 
-! Wrap everything in a catch which starts a listener so
-! you can see what went wrong, instead of dealing with a
-! fep
-
 ! We time bootstrap
 millis >r
 
diff --git a/core/classes/algebra/algebra-docs.factor b/core/classes/algebra/algebra-docs.factor
index 87c72048f4..3903da1ebc 100755
--- a/core/classes/algebra/algebra-docs.factor
+++ b/core/classes/algebra/algebra-docs.factor
@@ -1,14 +1,14 @@
-USING: help.markup help.syntax kernel classes ;
+USING: help.markup help.syntax kernel classes words
+checksums checksums.crc32 sequences math ;
 IN: classes.algebra
 
 ARTICLE: "class-operations" "Class operations"
 "Set-theoretic operations on classes:"
 { $subsection class< }
+{ $subsection class<= }
 { $subsection class-and }
 { $subsection class-or }
 { $subsection classes-intersect? }
-"Topological sort:"
-{ $subsection sort-classes }
 { $subsection min-class }
 "Low-level implementation detail:"
 { $subsection class-types }
@@ -17,6 +17,40 @@ ARTICLE: "class-operations" "Class operations"
 { $subsection class-types }
 { $subsection class-tags } ;
 
+ARTICLE: "class-linearization" "Class linearization"
+"Classes have an intrinsic partial order; given two classes A and B, we either have that A is a subset of B, B is a subset of A, A and B are equal as sets, or they are incomparable. The last two situations present difficulties for method dispatch:"
+{ $list
+    "If a generic word defines a method on a mixin class A and another class B, and B is the only instance of A, there is an ambiguity because A and B are equal as sets; any object that is an instance of one is an instance of both."
+    { "If a generic word defines methods on two union classes which are incomparable but not disjoint, for example " { $link sequence } " and " { $link number } ", there is an ambiguity because the generic word may be called on an object that is an instance of both unions." }
+}
+"These difficulties are resolved by imposing a linear order on classes, computed as follows for two classes A and B:"
+{ $list
+    "If A and B are the same class (not just equal as sets), then comparison stops."
+    "If A is a proper subset of B, or B is a proper subset of A, then comparison stops."
+    { "Next, the metaclasses of A and B are compared, with intrinsic meta-class order, from most-specific to least-specific:"
+        { $list
+            "Built-in classes and tuple classes"
+            "Predicate classes"
+            "Union classes"
+            "Mixin classes"
+        }
+    "If this yields an unambiguous answer, comparison stops."
+    }
+    "If the metaclasses of A and B occupy the same position in the order, then the vocabularies of A and B are compared lexicographically. If this yields an unambiguous answer, comparison stops."
+    "If A and B belong to the same vocabulary, their names are compared lexicographically. This must yield an unambiguous result, since if the names equal they must be the same class and this case was already handled in the first step."
+}
+"Some examples:"
+{ $list
+    { { $link integer } " precedes " { $link number } " because it is a strict subset" }
+    { { $link number } " precedes " { $link sequence } " because the " { $vocab-link "math" } " vocabulary precedes the " { $vocab-link "sequences" } " vocabulary" }
+    { { $link crc32 } " precedes " { $link checksum } ", even if it were the only instance, because " { $link crc32 } " is a singleton class which is more specific than a mixin class" }
+}
+"Operations:"
+{ $subsection class<=> }
+{ $subsection sort-classes }
+"Metaclass order:"
+{ $subsection rank-class } ;
+
 HELP: flatten-builtin-class
 { $values { "class" class } { "assoc" "an assoc whose keys are classes" } }
 { $description "Outputs a set of tuple classes whose union is the smallest cover of " { $snippet "class" } " intersected with " { $link tuple } "." } ;
@@ -29,14 +63,16 @@ HELP: class-types
 { $values { "class" class } { "seq" "an increasing sequence of integers" } }
 { $description "Outputs a sequence of builtin type numbers whose instances can possibly be instances of the given class." } ;
 
-HELP: class<
+HELP: class<=
 { $values { "first" "a class" } { "second" "a class" } { "?" "a boolean" } }
 { $description "Tests if all instances of " { $snippet "class1" } " are also instances of " { $snippet "class2" } "." }
 { $notes "Classes are partially ordered. This means that if " { $snippet "class1 <= class2" } " and " { $snippet "class2 <= class1" } ", then " { $snippet "class1 = class2" } ". Also, if " { $snippet "class1 <= class2" } " and " { $snippet "class2 <= class3" } ", then " { $snippet "class1 <= class3" } "." } ;
 
 HELP: sort-classes
 { $values { "seq" "a sequence of class" } { "newseq" "a new seqence of classes" } }
-{ $description "Outputs a topological sort of a sequence of classes. Larger classes come before their subclasses." } ;
+{ $description "Outputs a linear sort of a sequence of classes. Larger classes come before their subclasses." } ;
+
+{ sort-classes class<=> } related-words
 
 HELP: class-or
 { $values { "first" class } { "second" class } { "class" class } }
@@ -53,3 +89,7 @@ HELP: classes-intersect?
 HELP: min-class
 { $values { "class" class } { "seq" "a sequence of class words" } { "class/f" "a class word or " { $link f } } }
 { $description "If all classes in " { $snippet "seq" } " that intersect " { $snippet "class" } " are subtypes of " { $snippet "class" } ", outputs the last such element of " { $snippet "seq" } ". If any conditions fail to hold, outputs " { $link f } "." } ;
+
+HELP: class<=>
+{ $values { "first" class } { "second" class } { "n" symbol } }
+{ $description "Compares two classes with the class linearization order." } ;
diff --git a/core/classes/algebra/algebra-tests.factor b/core/classes/algebra/algebra-tests.factor
index dba97c16f5..7387b8ae3a 100755
--- a/core/classes/algebra/algebra-tests.factor
+++ b/core/classes/algebra/algebra-tests.factor
@@ -4,9 +4,9 @@ kernel math namespaces parser prettyprint sequences strings
 tools.test vectors words quotations classes classes.algebra
 classes.private classes.union classes.mixin classes.predicate
 vectors definitions source-files compiler.units growable
-random inference effects kernel.private sbufs ;
+random inference effects kernel.private sbufs math.order ;
 
-: class= [ class< ] 2keep swap class< and ;
+: class= [ class<= ] [ swap class<= ] 2bi and ;
 
 : class-and* >r class-and r> class= ;
 
@@ -38,43 +38,43 @@ UNION: both first-one union-class ;
 
 [ f ] [ number vector class-and sequence classes-intersect? ] unit-test
 
-[ t ] [ \ fixnum \ integer class< ] unit-test
-[ t ] [ \ fixnum \ fixnum class< ] unit-test
-[ f ] [ \ integer \ fixnum class< ] unit-test
-[ t ] [ \ integer \ object class< ] unit-test
-[ f ] [ \ integer \ null class< ] unit-test
-[ t ] [ \ null \ object class< ] unit-test
+[ t ] [ \ fixnum \ integer class<= ] unit-test
+[ t ] [ \ fixnum \ fixnum class<= ] unit-test
+[ f ] [ \ integer \ fixnum class<= ] unit-test
+[ t ] [ \ integer \ object class<= ] unit-test
+[ f ] [ \ integer \ null class<= ] unit-test
+[ t ] [ \ null \ object class<= ] unit-test
 
-[ t ] [ \ generic \ word class< ] unit-test
-[ f ] [ \ word \ generic class< ] unit-test
+[ t ] [ \ generic \ word class<= ] unit-test
+[ f ] [ \ word \ generic class<= ] unit-test
 
-[ f ] [ \ reversed \ slice class< ] unit-test
-[ f ] [ \ slice \ reversed class< ] unit-test
+[ f ] [ \ reversed \ slice class<= ] unit-test
+[ f ] [ \ slice \ reversed class<= ] unit-test
 
 PREDICATE: no-docs < word "documentation" word-prop not ;
 
 UNION: no-docs-union no-docs integer ;
 
-[ t ] [ no-docs no-docs-union class< ] unit-test
-[ f ] [ no-docs-union no-docs class< ] unit-test
+[ t ] [ no-docs no-docs-union class<= ] unit-test
+[ f ] [ no-docs-union no-docs class<= ] unit-test
 
 TUPLE: a ;
 TUPLE: b ;
 UNION: c a b ;
 
-[ t ] [ \ c \ tuple class< ] unit-test
-[ f ] [ \ tuple \ c class< ] unit-test
+[ t ] [ \ c \ tuple class<= ] unit-test
+[ f ] [ \ tuple \ c class<= ] unit-test
 
-[ t ] [ \ tuple-class \ class class< ] unit-test
-[ f ] [ \ class \ tuple-class class< ] unit-test
+[ t ] [ \ tuple-class \ class class<= ] unit-test
+[ f ] [ \ class \ tuple-class class<= ] unit-test
 
 TUPLE: tuple-example ;
 
-[ t ] [ \ null \ tuple-example class< ] unit-test
-[ f ] [ \ object \ tuple-example class< ] unit-test
-[ f ] [ \ object \ tuple-example class< ] unit-test
-[ t ] [ \ tuple-example \ tuple class< ] unit-test
-[ f ] [ \ tuple \ tuple-example class< ] unit-test
+[ t ] [ \ null \ tuple-example class<= ] unit-test
+[ f ] [ \ object \ tuple-example class<= ] unit-test
+[ f ] [ \ object \ tuple-example class<= ] unit-test
+[ t ] [ \ tuple-example \ tuple class<= ] unit-test
+[ f ] [ \ tuple \ tuple-example class<= ] unit-test
 
 TUPLE: a1 ;
 TUPLE: b1 ;
@@ -84,57 +84,57 @@ UNION: x1 a1 b1 ;
 UNION: y1 a1 c1 ;
 UNION: z1 b1 c1 ;
 
-[ f ] [ z1 x1 y1 class-and class< ] unit-test
+[ f ] [ z1 x1 y1 class-and class<= ] unit-test
 
-[ t ] [ x1 y1 class-and a1 class< ] unit-test
+[ t ] [ x1 y1 class-and a1 class<= ] unit-test
 
 [ f ] [ y1 z1 class-and x1 classes-intersect? ] unit-test
 
-[ f ] [ b1 c1 class-or a1 b1 class-or a1 c1 class-and class-and class< ] unit-test
+[ f ] [ b1 c1 class-or a1 b1 class-or a1 c1 class-and class-and class<= ] unit-test
 
-[ t ] [ a1 b1 class-or a1 c1 class-or class-and a1 class< ] unit-test
+[ t ] [ a1 b1 class-or a1 c1 class-or class-and a1 class<= ] unit-test
 
 [ f ] [ a1 c1 class-or b1 c1 class-or class-and a1 b1 class-or classes-intersect? ] unit-test
 
 [ f ] [ growable \ hi-tag classes-intersect? ] unit-test
 
 [ t ] [
-    growable tuple sequence class-and class<
+    growable tuple sequence class-and class<=
 ] unit-test
 
 [ t ] [
-    growable assoc class-and tuple class<
+    growable assoc class-and tuple class<=
 ] unit-test
 
-[ t ] [ object \ f \ f class-not class-or class< ] unit-test
+[ t ] [ object \ f \ f class-not class-or class<= ] unit-test
 
 [ t ] [ fixnum class-not integer class-and bignum class= ] unit-test
 
 [ f ] [ integer integer class-not classes-intersect? ] unit-test
 
-[ t ] [ array number class-not class< ] unit-test
+[ t ] [ array number class-not class<= ] unit-test
 
-[ f ] [ bignum number class-not class< ] unit-test
+[ f ] [ bignum number class-not class<= ] unit-test
 
 [ vector ] [ vector class-not class-not ] unit-test
 
-[ t ] [ fixnum fixnum bignum class-or class< ] unit-test
+[ t ] [ fixnum fixnum bignum class-or class<= ] unit-test
 
-[ f ] [ fixnum class-not integer class-and array class< ] unit-test
+[ f ] [ fixnum class-not integer class-and array class<= ] unit-test
 
-[ f ] [ fixnum class-not integer class< ] unit-test
+[ f ] [ fixnum class-not integer class<= ] unit-test
 
-[ f ] [ number class-not array class< ] unit-test
+[ f ] [ number class-not array class<= ] unit-test
 
-[ f ] [ fixnum class-not array class< ] unit-test
+[ f ] [ fixnum class-not array class<= ] unit-test
 
-[ t ] [ number class-not integer class-not class< ] unit-test
+[ t ] [ number class-not integer class-not class<= ] unit-test
 
 [ t ] [ vector array class-not class-and vector class= ] unit-test
 
 [ f ] [ fixnum class-not number class-and array classes-intersect? ] unit-test
 
-[ f ] [ fixnum class-not integer class< ] unit-test
+[ f ] [ fixnum class-not integer class<= ] unit-test
 
 [ t ] [ null class-not object class= ] unit-test
 
@@ -147,7 +147,7 @@ UNION: z1 b1 c1 ;
 [ t ] [
     fixnum class-not
     fixnum fixnum class-not class-or
-    class<
+    class<=
 ] unit-test
 
 ! Test method inlining
@@ -241,3 +241,14 @@ UNION: z1 b1 c1 ;
         =
     ] unit-test
 ] times
+
+SINGLETON: xxx
+UNION: yyy xxx ;
+
+[ { yyy xxx } ] [ { xxx yyy } sort-classes ] unit-test
+[ { yyy xxx } ] [ { yyy xxx } sort-classes ] unit-test
+
+[ { number integer ratio } ] [ { ratio number integer } sort-classes ] unit-test
+[ { sequence number ratio } ] [ { ratio number sequence } sort-classes ] unit-test
+
+[ +lt+ ] [ \ real sequence class<=> ] unit-test
diff --git a/core/classes/algebra/algebra.factor b/core/classes/algebra/algebra.factor
index 6a286e3204..8c910a1f8c 100755
--- a/core/classes/algebra/algebra.factor
+++ b/core/classes/algebra/algebra.factor
@@ -2,16 +2,16 @@
 ! See http://factorcode.org/license.txt for BSD license.
 USING: kernel classes classes.builtin combinators accessors
 sequences arrays vectors assocs namespaces words sorting layouts
-math hashtables kernel.private sets ;
+math hashtables kernel.private sets math.order ;
 IN: classes.algebra
 
 : 2cache ( key1 key2 assoc quot -- value )
     >r >r 2array r> [ first2 ] r> compose cache ; inline
 
-DEFER: (class<)
+DEFER: (class<=)
 
-: class< ( first second -- ? )
-    class<-cache get [ (class<) ] 2cache ;
+: class<= ( first second -- ? )
+    class<=-cache get [ (class<=) ] 2cache ;
 
 DEFER: (class-not)
 
@@ -45,31 +45,31 @@ TUPLE: anonymous-complement class ;
 
 C: <anonymous-complement> anonymous-complement
 
-: superclass< ( first second -- ? )
-    >r superclass r> class< ;
+: superclass<= ( first second -- ? )
+    >r superclass r> class<= ;
 
-: left-union-class< ( first second -- ? )
-    >r members r> [ class< ] curry all? ;
+: left-union-class<= ( first second -- ? )
+    >r members r> [ class<= ] curry all? ;
 
-: right-union-class< ( first second -- ? )
-    members [ class< ] with contains? ;
+: right-union-class<= ( first second -- ? )
+    members [ class<= ] with contains? ;
 
 : left-anonymous-union< ( first second -- ? )
-    >r members>> r> [ class< ] curry all? ;
+    >r members>> r> [ class<= ] curry all? ;
 
 : right-anonymous-union< ( first second -- ? )
-    members>> [ class< ] with contains? ;
+    members>> [ class<= ] with contains? ;
 
 : left-anonymous-intersection< ( first second -- ? )
-    >r members>> r> [ class< ] curry contains? ;
+    >r members>> r> [ class<= ] curry contains? ;
 
 : right-anonymous-intersection< ( first second -- ? )
-    members>> [ class< ] with all? ;
+    members>> [ class<= ] with all? ;
 
 : anonymous-complement< ( first second -- ? )
-    [ class>> ] bi@ swap class< ;
+    [ class>> ] bi@ swap class<= ;
 
-: (class<) ( first second -- -1/0/1 )  
+: (class<=) ( first second -- -1/0/1 )  
     {
         { [ 2dup eq? ] [ 2drop t ] }
         { [ dup object eq? ] [ 2drop t ] }
@@ -77,13 +77,13 @@ C: <anonymous-complement> anonymous-complement
         { [ 2dup [ anonymous-complement? ] both? ] [ anonymous-complement< ] }
         { [ over anonymous-union? ] [ left-anonymous-union< ] }
         { [ over anonymous-intersection? ] [ left-anonymous-intersection< ] }
-        { [ over members ] [ left-union-class< ] }
+        { [ over members ] [ left-union-class<= ] }
         { [ dup anonymous-union? ] [ right-anonymous-union< ] }
         { [ dup anonymous-intersection? ] [ right-anonymous-intersection< ] }
         { [ over anonymous-complement? ] [ 2drop f ] }
         { [ dup anonymous-complement? ] [ class>> classes-intersect? not ] }
-        { [ dup members ] [ right-union-class< ] }
-        { [ over superclass ] [ superclass< ] }
+        { [ dup members ] [ right-union-class<= ] }
+        { [ over superclass ] [ superclass<= ] }
         [ 2drop f ]
     } cond ;
 
@@ -94,7 +94,7 @@ C: <anonymous-complement> anonymous-complement
     members>> [ classes-intersect? ] with all? ;
 
 : anonymous-complement-intersect? ( first second -- ? )
-    class>> class< not ;
+    class>> class<= not ;
 
 : union-class-intersect? ( first second -- ? )
     members [ classes-intersect? ] with contains? ;
@@ -103,7 +103,7 @@ C: <anonymous-complement> anonymous-complement
     {
         { [ over tuple eq? ] [ 2drop t ] }
         { [ over builtin-class? ] [ 2drop f ] }
-        { [ over tuple-class? ] [ [ class< ] [ swap class< ] 2bi or ] }
+        { [ over tuple-class? ] [ [ class<= ] [ swap class<= ] 2bi or ] }
         [ swap classes-intersect? ]
     } cond ;
 
@@ -145,8 +145,8 @@ C: <anonymous-complement> anonymous-complement
 
 : (class-and) ( first second -- class )
     {
-        { [ 2dup class< ] [ drop ] }
-        { [ 2dup swap class< ] [ nip ] }
+        { [ 2dup class<= ] [ drop ] }
+        { [ 2dup swap class<= ] [ nip ] }
         { [ 2dup classes-intersect? not ] [ 2drop null ] }
         { [ dup members ] [ right-union-and ] }
         { [ dup anonymous-union? ] [ right-anonymous-union-and ] }
@@ -165,8 +165,8 @@ C: <anonymous-complement> anonymous-complement
 
 : (class-or) ( first second -- class )
     {
-        { [ 2dup class< ] [ nip ] }
-        { [ 2dup swap class< ] [ drop ] }
+        { [ 2dup class<= ] [ nip ] }
+        { [ 2dup swap class<= ] [ drop ] }
         { [ dup anonymous-union? ] [ right-anonymous-union-or ] }
         { [ over anonymous-union? ] [ left-anonymous-union-or ] }
         [ 2array <anonymous-union> ]
@@ -180,22 +180,43 @@ C: <anonymous-complement> anonymous-complement
         [ <anonymous-complement> ]
     } cond ;
 
-: largest-class ( seq -- n elt )
-    dup [
-        [ 2dup class< >r swap class< not r> and ]
-        with filter empty?
-    ] curry find [ "Topological sort failed" throw ] unless* ;
+: class< ( first second -- ? )
+    {
+        { [ 2dup class<= not ] [ 2drop f ] }
+        { [ 2dup swap class<= not ] [ 2drop t ] }
+        [ [ rank-class ] bi@ < ]
+    } cond ;
+
+: class-tie-breaker ( first second -- n )
+    2dup [ rank-class ] compare {
+        { +lt+ [ 2drop +lt+ ] }
+        { +gt+ [ 2drop +gt+ ] }
+        { +eq+ [ <=> ] }
+    } case ;
+
+: (class<=>) ( first second -- n )
+    {
+        { [ 2dup class<= ] [
+            2dup swap class<=
+            [ class-tie-breaker ] [ 2drop +lt+ ] if
+        ] }
+        { [ 2dup swap class<= ] [
+            2dup class<=
+            [ class-tie-breaker ] [ 2drop +gt+ ] if
+        ] }
+        [ class-tie-breaker ]
+    } cond ;
+
+: class<=> ( first second -- n )
+    class<=>-cache get [ (class<=>) ] 2cache ;
 
 : sort-classes ( seq -- newseq )
-    >vector
-    [ dup empty? not ]
-    [ dup largest-class >r over delete-nth r> ]
-    [ ] unfold nip ;
+    [ class<=> invert-comparison ] sort ;
 
 : min-class ( class seq -- class/f )
     over [ classes-intersect? ] curry filter
     dup empty? [ 2drop f ] [
-        tuck [ class< ] with all? [ peek ] [ drop f ] if
+        tuck [ class<= ] with all? [ peek ] [ drop f ] if
     ] if ;
 
 : (flatten-class) ( class -- )
@@ -212,7 +233,7 @@ C: <anonymous-complement> anonymous-complement
 
 : flatten-builtin-class ( class -- assoc )
     flatten-class [
-        dup tuple class< [ 2drop tuple tuple ] when
+        dup tuple class<= [ 2drop tuple tuple ] when
     ] assoc-map ;
 
 : class-types ( class -- seq )
diff --git a/core/classes/builtin/builtin.factor b/core/classes/builtin/builtin.factor
index 1c2871b031..8e992b852e 100644
--- a/core/classes/builtin/builtin.factor
+++ b/core/classes/builtin/builtin.factor
@@ -16,3 +16,5 @@ PREDICATE: builtin-class < class
 M: hi-tag class hi-tag type>class ;
 
 M: object class tag type>class ;
+
+M: builtin-class rank-class drop 0 ;
diff --git a/core/classes/classes-docs.factor b/core/classes/classes-docs.factor
index 5971ffd9fa..744944c281 100755
--- a/core/classes/classes-docs.factor
+++ b/core/classes/classes-docs.factor
@@ -47,6 +47,7 @@ $nl
 $nl
 "Classes can be inspected and operated upon:"
 { $subsection "class-operations" }
+{ $subsection "class-linearization" }
 { $see-also "class-index" } ;
 
 ABOUT: "classes"
diff --git a/core/classes/classes-tests.factor b/core/classes/classes-tests.factor
index ae19f38d14..bb9fbd0167 100755
--- a/core/classes/classes-tests.factor
+++ b/core/classes/classes-tests.factor
@@ -18,14 +18,14 @@ GENERIC: generic-update-test ( x -- y )
 
 M: union-1 generic-update-test drop "union-1" ;
 
-[ f ] [ bignum union-1 class< ] unit-test
-[ t ] [ union-1 number class< ] unit-test
+[ f ] [ bignum union-1 class<= ] unit-test
+[ t ] [ union-1 number class<= ] unit-test
 [ "union-1" ] [ 1.0 generic-update-test ] unit-test
 
 "IN: classes.tests USE: math USE: arrays UNION: union-1 rational array ;" eval
 
-[ t ] [ bignum union-1 class< ] unit-test
-[ f ] [ union-1 number class< ] unit-test
+[ t ] [ bignum union-1 class<= ] unit-test
+[ f ] [ union-1 number class<= ] unit-test
 [ "union-1" ] [ { 1.0 } generic-update-test ] unit-test
 
 "IN: classes.tests USE: math PREDICATE: union-1 < integer even? ;" eval
@@ -52,7 +52,7 @@ M: sequence-mixin collection-size length ;
 
 M: assoc-mixin collection-size assoc-size ;
 
-[ t ] [ array sequence-mixin class< ] unit-test
+[ t ] [ array sequence-mixin class<= ] unit-test
 [ t ] [ { 1 2 3 } sequence-mixin? ] unit-test
 [ 3 ] [ { 1 2 3 } collection-size ] unit-test
 [ f ] [ H{ { 1 2 } { 2 3 } } sequence-mixin? ] unit-test
@@ -67,14 +67,14 @@ MIXIN: mx1
 
 INSTANCE: integer mx1
 
-[ t ] [ integer mx1 class< ] unit-test
-[ t ] [ mx1 integer class< ] unit-test
-[ t ] [ mx1 number class< ] unit-test
+[ t ] [ integer mx1 class<= ] unit-test
+[ t ] [ mx1 integer class<= ] unit-test
+[ t ] [ mx1 number class<= ] unit-test
 
 "IN: classes.tests USE: arrays INSTANCE: array mx1" eval
 
-[ t ] [ array mx1 class< ] unit-test
-[ f ] [ mx1 number class< ] unit-test
+[ t ] [ array mx1 class<= ] unit-test
+[ f ] [ mx1 number class<= ] unit-test
 
 [ \ mx1 forget ] with-compilation-unit
 
@@ -94,14 +94,14 @@ UNION: redefine-bug-1 fixnum ;
 
 UNION: redefine-bug-2 redefine-bug-1 quotation ;
 
-[ t ] [ fixnum redefine-bug-2 class< ] unit-test
-[ t ] [ quotation redefine-bug-2 class< ] unit-test
+[ t ] [ fixnum redefine-bug-2 class<= ] unit-test
+[ t ] [ quotation redefine-bug-2 class<= ] unit-test
 
 [ ] [ "IN: classes.tests USE: math UNION: redefine-bug-1 bignum ;" eval ] unit-test
 
-[ t ] [ bignum redefine-bug-1 class< ] unit-test
-[ f ] [ fixnum redefine-bug-2 class< ] unit-test
-[ t ] [ bignum redefine-bug-2 class< ] unit-test
+[ t ] [ bignum redefine-bug-1 class<= ] unit-test
+[ f ] [ fixnum redefine-bug-2 class<= ] unit-test
+[ t ] [ bignum redefine-bug-2 class<= ] unit-test
 
 USE: io.streams.string
 
diff --git a/core/classes/classes.factor b/core/classes/classes.factor
index c998a1b155..53840c0027 100755
--- a/core/classes/classes.factor
+++ b/core/classes/classes.factor
@@ -5,21 +5,24 @@ slots.private namespaces sequences strings words vectors math
 quotations combinators sorting effects graphs vocabs ;
 IN: classes
 
-SYMBOL: class<-cache
+SYMBOL: class<=-cache
+SYMBOL: class<=>-cache
 SYMBOL: class-not-cache
 SYMBOL: classes-intersect-cache
 SYMBOL: class-and-cache
 SYMBOL: class-or-cache
 
 : init-caches ( -- )
-    H{ } clone class<-cache set
+    H{ } clone class<=-cache set
+    H{ } clone class<=>-cache set
     H{ } clone class-not-cache set
     H{ } clone classes-intersect-cache set
     H{ } clone class-and-cache set
     H{ } clone class-or-cache set ;
 
 : reset-caches ( -- )
-    class<-cache get clear-assoc
+    class<=-cache get clear-assoc
+    class<=>-cache get clear-assoc
     class-not-cache get clear-assoc
     classes-intersect-cache get clear-assoc
     class-and-cache get clear-assoc
@@ -57,6 +60,8 @@ PREDICATE: predicate < word "predicating" word-prop >boolean ;
     #! Output f for non-classes to work with algebra code
     dup class? [ "members" word-prop ] [ drop f ] if ;
 
+GENERIC: rank-class ( class -- n )
+
 GENERIC: reset-class ( class -- )
 
 M: word reset-class drop ;
diff --git a/core/classes/mixin/mixin.factor b/core/classes/mixin/mixin.factor
index ca2547bacf..6f888ceca1 100755
--- a/core/classes/mixin/mixin.factor
+++ b/core/classes/mixin/mixin.factor
@@ -9,6 +9,8 @@ PREDICATE: mixin-class < union-class "mixin" word-prop ;
 M: mixin-class reset-class
     { "class" "metaclass" "members" "mixin" } reset-props ;
 
+M: mixin-class rank-class drop 3 ;
+
 : redefine-mixin-class ( class members -- )
     dupd define-union-class
     t "mixin" set-word-prop ;
diff --git a/core/classes/predicate/predicate.factor b/core/classes/predicate/predicate.factor
index 4729a6dd5e..4e4d1701e4 100755
--- a/core/classes/predicate/predicate.factor
+++ b/core/classes/predicate/predicate.factor
@@ -30,3 +30,5 @@ M: predicate-class reset-class
         "predicate-definition"
         "superclass"
     } reset-props ;
+
+M: predicate-class rank-class drop 1 ;
diff --git a/core/classes/tuple/tuple-tests.factor b/core/classes/tuple/tuple-tests.factor
index 41776c4eec..0cde687f16 100755
--- a/core/classes/tuple/tuple-tests.factor
+++ b/core/classes/tuple/tuple-tests.factor
@@ -233,8 +233,8 @@ TUPLE: laptop < computer battery ;
 C: <laptop> laptop
 
 [ t ] [ laptop tuple-class? ] unit-test
-[ t ] [ laptop tuple class< ] unit-test
-[ t ] [ laptop computer class< ] unit-test
+[ t ] [ laptop tuple class<= ] unit-test
+[ t ] [ laptop computer class<= ] unit-test
 [ t ] [ laptop computer classes-intersect? ] unit-test
 
 [ ] [ "Pentium" 128 3 hours <laptop> "laptop" set ] unit-test
@@ -266,8 +266,8 @@ TUPLE: server < computer rackmount ;
 C: <server> server
 
 [ t ] [ server tuple-class? ] unit-test
-[ t ] [ server tuple class< ] unit-test
-[ t ] [ server computer class< ] unit-test
+[ t ] [ server tuple class<= ] unit-test
+[ t ] [ server computer class<= ] unit-test
 [ t ] [ server computer classes-intersect? ] unit-test
 
 [ ] [ "PowerPC" 64 "1U" <server> "server" set ] unit-test
@@ -286,8 +286,8 @@ test-server-slot-values
 [ f ] [ "server" get laptop? ] unit-test
 [ f ] [ "laptop" get server? ] unit-test
 
-[ f ] [ server laptop class< ] unit-test
-[ f ] [ laptop server class< ] unit-test
+[ f ] [ server laptop class<= ] unit-test
+[ f ] [ laptop server class<= ] unit-test
 [ f ] [ laptop server classes-intersect? ] unit-test
 
 [ f ] [ 1 2 <computer> laptop? ] unit-test
@@ -306,9 +306,9 @@ TUPLE: electronic-device ;
 
 [ ] [ "IN: classes.tuple.tests TUPLE: computer < electronic-device cpu ram ;" eval ] unit-test
 
-[ f ] [ electronic-device laptop class< ] unit-test
-[ t ] [ server electronic-device class< ] unit-test
-[ t ] [ laptop server class-or electronic-device class< ] unit-test
+[ f ] [ electronic-device laptop class<= ] unit-test
+[ t ] [ server electronic-device class<= ] unit-test
+[ t ] [ laptop server class-or electronic-device class<= ] unit-test
 
 [ t ] [ "laptop" get electronic-device? ] unit-test
 [ t ] [ "laptop" get computer? ] unit-test
diff --git a/core/classes/tuple/tuple.factor b/core/classes/tuple/tuple.factor
index 8bcf023131..ee7ff8c608 100755
--- a/core/classes/tuple/tuple.factor
+++ b/core/classes/tuple/tuple.factor
@@ -226,6 +226,8 @@ M: tuple-class reset-class
         } reset-props
     ] bi ;
 
+M: tuple-class rank-class drop 0 ;
+
 M: tuple clone
     (clone) dup delegate clone over set-delegate ;
 
diff --git a/core/classes/union/union.factor b/core/classes/union/union.factor
index 09f8f88ced..760844afb9 100755
--- a/core/classes/union/union.factor
+++ b/core/classes/union/union.factor
@@ -30,3 +30,5 @@ M: union-class update-class define-union-predicate ;
 
 M: union-class reset-class
     { "class" "metaclass" "members" } reset-props ;
+
+M: union-class rank-class drop 2 ;
diff --git a/core/generator/registers/registers.factor b/core/generator/registers/registers.factor
index e0fd7bd457..c5e1ea54a6 100755
--- a/core/generator/registers/registers.factor
+++ b/core/generator/registers/registers.factor
@@ -181,11 +181,11 @@ INSTANCE: constant value
 
 : %unbox-c-ptr ( dst src -- )
     dup operand-class {
-        { [ dup \ f class< ] [ drop %unbox-f ] }
-        { [ dup simple-alien class< ] [ drop %unbox-alien ] }
-        { [ dup byte-array class< ] [ drop %unbox-byte-array ] }
-        { [ dup bit-array class< ] [ drop %unbox-byte-array ] }
-        { [ dup float-array class< ] [ drop %unbox-byte-array ] }
+        { [ dup \ f class<= ] [ drop %unbox-f ] }
+        { [ dup simple-alien class<= ] [ drop %unbox-alien ] }
+        { [ dup byte-array class<= ] [ drop %unbox-byte-array ] }
+        { [ dup bit-array class<= ] [ drop %unbox-byte-array ] }
+        { [ dup float-array class<= ] [ drop %unbox-byte-array ] }
         [ drop %unbox-any-c-ptr ]
     } cond ; inline
 
@@ -569,7 +569,7 @@ M: loc lazy-store
     {
         { f [ drop t ] }
         { known-tag [ class-tag >boolean ] }
-        [ class< ]
+        [ class<= ]
     } case ;
 
 : spec-matches? ( value spec -- ? )
@@ -644,7 +644,7 @@ PRIVATE>
 UNION: immediate fixnum POSTPONE: f ;
 
 : operand-immediate? ( operand -- ? )
-    operand-class immediate class< ;
+    operand-class immediate class<= ;
 
 : phantom-push ( obj -- )
     1 phantom-datastack get adjust-phantom
diff --git a/core/generic/generic-docs.factor b/core/generic/generic-docs.factor
index 1024c377a8..39293bfec9 100755
--- a/core/generic/generic-docs.factor
+++ b/core/generic/generic-docs.factor
@@ -4,22 +4,22 @@ generic.standard generic.math combinators ;
 IN: generic
 
 ARTICLE: "method-order" "Method precedence"
-"Consider the case where a generic word has methods on two classes, say A and B, which share a non-empty intersection. If the generic word is called on an object which is an instance of both A and B, a choice of method must be made. If A is a subclass of B, the method for A to be called; this makes sense, because we're defining general behavior for instances of B, and refining it for instances of A. Conversely, if B is a subclass of A, then we expect B's method to be called. However, if neither is a subclass of the other, we have an ambiguous situation and undefined behavior will result. Either the method for A or B will be called, and there is no way to predict ahead of time."
-$nl
-"The generic word system linearly orders all the methods on a generic word by their class. Conceptually, method dispatch is implemented by testing the object against the predicate word for every class, in order. If methods are defined on overlapping classes, this order will fail to be unique and the problem described above can occur."
+"Conceptually, method dispatch is implemented by testing the object against the predicate word for every class, in linear order (" { $link "class-linearization" } ")."
 $nl
 "Here is an example:"
 { $code
     "GENERIC: explain"
-    "M: number explain drop \"an integer\" print ;"
-    "M: sequence explain drop \"a sequence\" print ;"
     "M: object explain drop \"an object\" print ;"
+    "M: number explain drop \"a number\" print ;"
+    "M: sequence explain drop \"a sequence\" print ;"
 }
-"Neither " { $link number } " nor " { $link sequence } " are subclasses of each other, yet their intersection is the non-empty " { $link integer } " class. As a result, the outcome of calling " { $snippet "bar" } " with an " { $link integer } " on the stack is undefined - either one of the two methods may be called. This situation can lead to subtle bugs. To avoid it, explicitly disambiguate the method order by defining a method on the intersection. If in this case we want integers to behave like numbers, we would also define:"
-{ $code "M: integer explain drop \"an integer\" print ;" }
-"On the other hand, if we want integers to behave like sequences here, we could define:"
+"The linear order is the following, from least-specific to most-specific:"
+{ $code "{ object sequence number }" }
+"Neither " { $link number } " nor " { $link sequence } " are subclasses of each other, yet their intersection is the non-empty " { $link integer } " class. Calling " { $snippet "explain" } " with an integer on the stack will print " { $snippet "a number" } " because " { $link number } " precedes " { $link sequence } " in the class linearization order. If this was not the desired outcome, define a method on the intersection:"
 { $code "M: integer explain drop \"a sequence\" print ;" }
-"The " { $link order } " word can be useful to clarify method dispatch order."
+"Now, the linear order is the following, from least-specific to most-specific:"
+{ $code "{ object sequence number integer }" }
+"The " { $link order } " word can be useful to clarify method dispatch order:"
 { $subsection order } ;
 
 ARTICLE: "generic-introspection" "Generic word introspection"
diff --git a/core/generic/generic.factor b/core/generic/generic.factor
index 82bab475b3..d35ba01e52 100755
--- a/core/generic/generic.factor
+++ b/core/generic/generic.factor
@@ -35,7 +35,7 @@ PREDICATE: method-spec < pair
 GENERIC: effective-method ( ... generic -- method )
 
 : next-method-class ( class generic -- class/f )
-    order [ class< ] with filter reverse dup length 1 =
+    order [ class<= ] with filter reverse dup length 1 =
     [ drop f ] [ second ] if ;
 
 : next-method ( class generic -- class/f )
diff --git a/core/generic/math/math.factor b/core/generic/math/math.factor
index 90590fe565..1c1368a6c2 100755
--- a/core/generic/math/math.factor
+++ b/core/generic/math/math.factor
@@ -10,14 +10,14 @@ PREDICATE: math-class < class
     dup null bootstrap-word eq? [
         drop f
     ] [
-        number bootstrap-word class<
+        number bootstrap-word class<=
     ] if ;
 
 : last/first ( seq -- pair ) [ peek ] [ first ] bi 2array ;
 
 : math-precedence ( class -- pair )
     {
-        { [ dup null class< ] [ drop { -1 -1 } ] }
+        { [ dup null class<= ] [ drop { -1 -1 } ] }
         { [ dup math-class? ] [ class-types last/first ] }
         [ drop { 100 100 } ]
     } cond ;
diff --git a/core/generic/standard/engines/engines.factor b/core/generic/standard/engines/engines.factor
index c09f1abfd4..20e22fde82 100644
--- a/core/generic/standard/engines/engines.factor
+++ b/core/generic/standard/engines/engines.factor
@@ -26,8 +26,8 @@ M: method-body engine>quot 1quotation ;
     alist>quot ;
 
 : split-methods ( assoc class -- first second )
-    [ [ nip class< not ] curry assoc-filter ]
-    [ [ nip class<     ] curry assoc-filter ] 2bi ;
+    [ [ nip class<= not ] curry assoc-filter ]
+    [ [ nip class<=     ] curry assoc-filter ] 2bi ;
 
 : convert-methods ( assoc class word -- assoc' )
     over >r >r split-methods dup assoc-empty? [
diff --git a/core/generic/standard/engines/predicate/predicate.factor b/core/generic/standard/engines/predicate/predicate.factor
index e4643b2f3d..b1bfc659df 100644
--- a/core/generic/standard/engines/predicate/predicate.factor
+++ b/core/generic/standard/engines/predicate/predicate.factor
@@ -11,7 +11,7 @@ C: <predicate-dispatch-engine> predicate-dispatch-engine
     [ >r "predicate" word-prop picker prepend r> ] assoc-map ;
 
 : keep-going? ( assoc -- ? )
-    assumed get swap second first class< ;
+    assumed get swap second first class<= ;
 
 : prune-redundant-predicates ( assoc -- default assoc' )
     {
diff --git a/core/inference/class/class.factor b/core/inference/class/class.factor
index 9d0c55afeb..933710aaca 100755
--- a/core/inference/class/class.factor
+++ b/core/inference/class/class.factor
@@ -143,7 +143,7 @@ M: literal-constraint constraint-satisfied?
     [ swap literal>> eql? ] [ 2drop f ] if ;
 
 M: class-constraint constraint-satisfied?
-    [ value>> value-class* ] [ class>> ] bi class< ;
+    [ value>> value-class* ] [ class>> ] bi class<= ;
 
 M: pair apply-constraint
     first2 2dup constraints get set-at
diff --git a/core/math/math.factor b/core/math/math.factor
index d5040757d4..0218ded6ff 100755
--- a/core/math/math.factor
+++ b/core/math/math.factor
@@ -80,9 +80,6 @@ M: number equal? number= ;
 
 M: real hashcode* nip >fixnum ;
 
-! real and sequence overlap. we disambiguate:
-M: integer hashcode* nip >fixnum ;
-
 GENERIC: fp-nan? ( x -- ? )
 
 M: object fp-nan?
diff --git a/core/math/order/order.factor b/core/math/order/order.factor
index 7cbef68dcc..76fe058ffa 100644
--- a/core/math/order/order.factor
+++ b/core/math/order/order.factor
@@ -7,17 +7,13 @@ SYMBOL: +lt+
 SYMBOL: +eq+
 SYMBOL: +gt+
 
-GENERIC: <=> ( obj1 obj2 -- symbol )
-
-: (<=>) ( a b -- symbol )
-    2dup < [ 2drop +lt+ ] [ number= +eq+ +gt+ ? ] if ; inline
-
 : invert-comparison ( symbol -- new-symbol )
     #! Can't use case, index or nth here
     dup +lt+ eq? [ drop +gt+ ] [ +eq+ eq? +eq+ +lt+ ? ] if ;
 
-M: real <=> (<=>) ;
-M: integer <=> (<=>) ;
+GENERIC: <=> ( obj1 obj2 -- symbol )
+
+M: real <=> 2dup < [ 2drop +lt+ ] [ number= +eq+ +gt+ ? ] if ;
 
 GENERIC: before? ( obj1 obj2 -- ? )
 GENERIC: after? ( obj1 obj2 -- ? )
diff --git a/core/optimizer/control/control.factor b/core/optimizer/control/control.factor
index de7aec2bb1..7ab0ffc806 100755
--- a/core/optimizer/control/control.factor
+++ b/core/optimizer/control/control.factor
@@ -154,9 +154,9 @@ SYMBOL: potential-loops
         node-literal t
     ] [
         node-class {
-            { [ dup null class< ] [ drop f f ] }
-            { [ dup \ f class-not class< ] [ drop t t ] }
-            { [ dup \ f class< ] [ drop f t ] }
+            { [ dup null class<= ] [ drop f f ] }
+            { [ dup \ f class-not class<= ] [ drop t t ] }
+            { [ dup \ f class<= ] [ drop f t ] }
             [ drop f f ]
         } cond
     ] if ;
diff --git a/core/optimizer/inlining/inlining.factor b/core/optimizer/inlining/inlining.factor
index 33c8244b4c..393264e459 100755
--- a/core/optimizer/inlining/inlining.factor
+++ b/core/optimizer/inlining/inlining.factor
@@ -77,7 +77,7 @@ DEFER: (flat-length)
         float real
         complex number
         object
-    } [ class< ] with find nip ;
+    } [ class<= ] with find nip ;
 
 : inlining-math-method ( #call word -- quot/f )
     swap node-input-classes
@@ -111,7 +111,7 @@ DEFER: (flat-length)
 : comparable? ( actual testing -- ? )
     #! If actual is a subset of testing or if the two classes
     #! are disjoint, return t.
-    2dup class< >r classes-intersect? not r> or ;
+    2dup class<= >r classes-intersect? not r> or ;
 
 : optimize-predicate? ( #call -- ? )
     dup node-param "predicating" word-prop dup [
@@ -132,7 +132,7 @@ DEFER: (flat-length)
 
 : evaluate-predicate ( #call -- ? )
     dup node-param "predicating" word-prop >r
-    node-class-first r> class< ;
+    node-class-first r> class<= ;
 
 : optimize-predicate ( #call -- node )
     #! If the predicate is followed by a branch we fold it
diff --git a/core/optimizer/math/math.factor b/core/optimizer/math/math.factor
index ab8a1f3eda..72e64d5b95 100755
--- a/core/optimizer/math/math.factor
+++ b/core/optimizer/math/math.factor
@@ -96,7 +96,7 @@ optimizer.math.partial generic.standard system accessors ;
 
 : math-closure ( class -- newclass )
     { null fixnum bignum integer rational float real number }
-    [ class< ] with find nip number or ;
+    [ class<= ] with find nip number or ;
 
 : fits? ( interval class -- ? )
     "interval" word-prop dup
@@ -108,7 +108,7 @@ optimizer.math.partial generic.standard system accessors ;
     dup r> at swap or ;
 
 : won't-overflow? ( interval node -- ? )
-    node-in-d [ value-class* fixnum class< ] all?
+    node-in-d [ value-class* fixnum class<= ] all?
     swap fixnum fits? and ;
 
 : post-process ( class interval node -- classes intervals )
@@ -214,7 +214,7 @@ optimizer.math.partial generic.standard system accessors ;
 : twiddle-interval ( i1 -- i2 )
     dup [
         node get node-in-d
-        [ value-class* integer class< ] all?
+        [ value-class* integer class<= ] all?
         [ integral-closure ] when
     ] when ;
 
@@ -293,7 +293,7 @@ most-negative-fixnum most-positive-fixnum [a,b]
 ! Removing overflow checks
 : remove-overflow-check? ( #call -- ? )
     dup out-d>> first node-class
-    [ fixnum class< ] [ null eq? not ] bi and ;
+    [ fixnum class<= ] [ null eq? not ] bi and ;
 
 {
     { + [ fixnum+fast ] }
@@ -356,7 +356,7 @@ most-negative-fixnum most-positive-fixnum [a,b]
     dup #call? [ node-param eq? ] [ 2drop f ] if ;
 
 : coerced-to-fixnum? ( #call -- ? )
-    dup dup node-in-d [ node-class integer class< ] with all?
+    dup dup node-in-d [ node-class integer class<= ] with all?
     [ \ >fixnum consumed-by? ] [ drop f ] if ;
 
 {
@@ -377,7 +377,7 @@ most-negative-fixnum most-positive-fixnum [a,b]
 
 : convert-rem-to-and? ( #call -- ? )
     dup node-in-d {
-        { [ 2dup first node-class integer class< not ] [ f ] }
+        { [ 2dup first node-class integer class<= not ] [ f ] }
         { [ 2dup second node-literal integer? not ] [ f ] }
         { [ 2dup second node-literal power-of-2? not ] [ f ] }
         [ t ]
diff --git a/core/optimizer/pattern-match/pattern-match.factor b/core/optimizer/pattern-match/pattern-match.factor
index 5beb2555f0..51fa254a25 100755
--- a/core/optimizer/pattern-match/pattern-match.factor
+++ b/core/optimizer/pattern-match/pattern-match.factor
@@ -12,7 +12,7 @@ SYMBOL: @
     @ get [ eq? ] [ @ set t ] if* ;
 
 : match-class ( value spec -- ? )
-    >r node get swap node-class r> class< ;
+    >r node get swap node-class r> class<= ;
 
 : value-match? ( value spec -- ? )
     {
diff --git a/extra/db/pooling/pooling-tests.factor b/extra/db/pooling/pooling-tests.factor
new file mode 100644
index 0000000000..7b0de65ac4
--- /dev/null
+++ b/extra/db/pooling/pooling-tests.factor
@@ -0,0 +1,8 @@
+IN: db.pooling.tests
+USING: db.pooling tools.test ;
+
+\ <pool> must-infer
+
+{ 2 0 } [ [ ] with-db-pool ] must-infer-as
+
+{ 1 0 } [ [ ] with-pooled-connection ] must-infer-as
diff --git a/extra/db/pooling/pooling.factor b/extra/db/pooling/pooling.factor
new file mode 100644
index 0000000000..83820294d6
--- /dev/null
+++ b/extra/db/pooling/pooling.factor
@@ -0,0 +1,43 @@
+! Copyright (C) 2008 Slava Pestov.
+! See http://factorcode.org/license.txt for BSD license.
+USING: accessors kernel arrays namespaces sequences continuations
+destructors db ;
+IN: db.pooling
+
+TUPLE: pool db params connections ;
+
+: <pool> ( db params -- pool )
+    V{ } clone pool boa ;
+
+M: pool dispose [ dispose-each f ] change-connections drop ;
+
+: with-db-pool ( db params quot -- )
+    >r <pool> r> [ pool swap with-variable ] curry with-disposal ; inline
+
+TUPLE: return-connection db pool ;
+
+: return-connection ( db pool -- )
+    connections>> push ;
+
+: new-connection ( pool -- )
+    [ [ db>> ] [ params>> ] bi make-db db-open ] keep
+    return-connection ;
+
+: acquire-connection ( pool -- db )
+    [ dup connections>> empty? ] [ dup new-connection ] [ ] while
+    connections>> pop ;
+
+: (with-pooled-connection) ( db pool quot -- )
+    [ >r drop db r> with-variable ]
+    [ drop return-connection ]
+    3bi ; inline
+
+: with-pooled-connection ( pool quot -- )
+    >r [ acquire-connection ] keep r>
+    [ (with-pooled-connection) ] [ ] [ 2drop dispose ] cleanup ; inline
+
+M: return-connection dispose
+    [ db>> ] [ pool>> ] bi return-connection ;
+
+: return-connection-later ( db pool -- )
+    \ return-connection boa add-always-destructor ;
diff --git a/extra/json/writer/writer.factor b/extra/json/writer/writer.factor
index 6ad0774e38..a68c65087e 100644
--- a/extra/json/writer/writer.factor
+++ b/extra/json/writer/writer.factor
@@ -21,11 +21,6 @@ M: string json-print ( obj -- )
 M: number json-print ( num -- )  
   number>string write ;
 
-! sequence and number overlap, we provide an explicit
-! disambiguation method
-M: integer json-print ( num -- )  
-  number>string write ;
-
 M: sequence json-print ( array -- ) 
   CHAR: [ write1 [ >json ] map "," join write CHAR: ] write1 ;
 
diff --git a/extra/multi-methods/multi-methods.factor b/extra/multi-methods/multi-methods.factor
index d5a698f5f8..59e8049232 100755
--- a/extra/multi-methods/multi-methods.factor
+++ b/extra/multi-methods/multi-methods.factor
@@ -86,12 +86,12 @@ SYMBOL: total
     [
         {
             { [ 2dup eq? ] [ +eq+ ] }
-            { [ 2dup [ class< ] 2keep swap class< and ] [ +eq+ ] }
-            { [ 2dup class< ] [ +lt+ ] }
-            { [ 2dup swap class< ] [ +gt+ ] }
+            { [ 2dup [ class<= ] [ swap class<= ] 2bi and ] [ +eq+ ] }
+            { [ 2dup class<= ] [ +lt+ ] }
+            { [ 2dup swap class<= ] [ +gt+ ] }
             [ +eq+ ]
         } cond 2nip
-    ] 2map [ zero? not ] find nip +eq+ or ;
+    ] 2map [ +eq+ eq? not ] find nip +eq+ or ;
 
 : sort-methods ( alist -- alist' )
     [ [ first ] bi@ classes< ] topological-sort ;
diff --git a/extra/tools/deploy/shaker/shaker.factor b/extra/tools/deploy/shaker/shaker.factor
index f95b83467a..1ad9957cc9 100755
--- a/extra/tools/deploy/shaker/shaker.factor
+++ b/extra/tools/deploy/shaker/shaker.factor
@@ -144,7 +144,8 @@ IN: tools.deploy.shaker
                 classes:class-and-cache
                 classes:class-not-cache
                 classes:class-or-cache
-                classes:class<-cache
+                classes:class<=-cache
+                classes:class<=>-cache
                 classes:classes-intersect-cache
                 classes:update-map
                 command-line:main-vocab-hook