diff --git a/examples/raytracer.factor b/examples/raytracer.factor
index b703fb69b0..e11f88f189 100644
--- a/examples/raytracer.factor
+++ b/examples/raytracer.factor
@@ -7,11 +7,7 @@ IN: ray
 ! parameters
 : light
     #! Normalized { -1 -3 2 }.
-    @{
-        -0.2672612419124244
-        -0.8017837257372732
-        0.5345224838248488
-    }@ ; inline
+    @{ -0.2672612419124244 -0.8017837257372732 0.5345224838248488 }@ ; inline
 
 : oversampling 4 ; inline
 
@@ -125,7 +121,7 @@ DEFER: create ( level c r -- scene )
     pick 1 = [ <sphere> nip ] [ create-group ] ifte ;
 
 : ss-point ( dx dy -- point )
-    >r oversampling /f r> oversampling /f 0.0 3array ;
+    [ oversampling /f ] 2apply 0.0 3array ;
 
 : ss-grid ( -- ss-grid )
     oversampling [ oversampling [ ss-point ] map-with ] map ;
@@ -142,14 +138,7 @@ DEFER: create ( level c r -- scene )
 : pixel-grid ( -- grid )
     size reverse [
         size [
-            size 0.5 * - swap size 0.5 * - size >float 3array
-        ] map-with
-    ] map ;
-
-: pixel-grid ( -- grid )
-    size reverse [
-        size [
-            size 0.5 * - swap size 0.5 * - size >float 3array
+            [ size 0.5 * - ] 2apply swap size >float 3array
         ] map-with
     ] map ;
 
diff --git a/library/bootstrap/boot-stage2.factor b/library/bootstrap/boot-stage2.factor
index 1a73358e0e..43aa7cdc0f 100644
--- a/library/bootstrap/boot-stage2.factor
+++ b/library/bootstrap/boot-stage2.factor
@@ -3,7 +3,7 @@
 USING: alien assembler command-line compiler compiler-backend
 errors generic hashtables io io-internals kernel
 kernel-internals lists math memory namespaces parser sequences
-words ;
+sequences-internals words ;
 
 : pull-in ( ? list -- )
     swap [
@@ -75,9 +75,11 @@ t [
 compile? [
     "Compiling base..." print
 
-    { car * length nth = string>number number>string scan (generate) }
-    [ compile ]
-    each
+    {
+        uncons 1+ 1- + <= > >= mod length
+        nth-unsafe set-nth-unsafe
+        = string>number number>string scan (generate)
+    } [ compile ] each
 ] when
 
 compile? [
diff --git a/library/bootstrap/image.factor b/library/bootstrap/image.factor
index fd83cc2b4f..1491501f1c 100644
--- a/library/bootstrap/image.factor
+++ b/library/bootstrap/image.factor
@@ -32,7 +32,7 @@ SYMBOL: 64-bits
     ] [
         dup 1 32 shift 1- bitand
         swap -32 shift 1 32 shift 1- bitand
-        big-endian get [ swap ] unless
+        big-endian get [ swap ] when
         emit emit
     ] ifte ;
 
diff --git a/library/collections/hashtables.factor b/library/collections/hashtables.factor
index b33c9c938c..1af3722f82 100644
--- a/library/collections/hashtables.factor
+++ b/library/collections/hashtables.factor
@@ -70,8 +70,7 @@ IN: hashtables
 
 : hash>alist ( hash -- alist )
     #! Push a list of key/value pairs in a hashtable.
-    [ ] swap [ hash-bucket [ swons ] each ] each-bucket ;
-    flushable
+    underlying concat ; flushable
 
 : (set-hash) ( value key hash -- )
     dup hash-size+ [ set-assoc ] set-hash* ;
diff --git a/library/collections/sequences-epilogue.factor b/library/collections/sequences-epilogue.factor
index f86e63d4d0..44dfa19f8b 100644
--- a/library/collections/sequences-epilogue.factor
+++ b/library/collections/sequences-epilogue.factor
@@ -36,6 +36,15 @@ M: object >list ( seq -- list ) dup length 0 rot (>list) ;
 : memq?   ( obj seq -- ? )     [ eq? ] contains-with? ; flushable
 : remove  ( obj list -- list ) [ = not ] subset-with ; flushable
 
+: (subst) ( newseq oldseq elt -- new/elt )
+    [ swap index ] keep
+    over -1 > [ drop swap nth ] [ 2nip ] ifte ;
+
+: subst ( newseq oldseq seq -- )
+    #! Mutates seq. If an element of seq occurs in oldseq,
+    #! replace it with the corresponding element in newseq.
+    [ >r 2dup r> (subst) ] inject 2drop ;
+
 : move ( to from seq -- )
     pick pick number=
     [ 3drop ] [ [ nth swap ] keep set-nth ] ifte ; inline
diff --git a/library/inference/branches.factor b/library/inference/branches.factor
index cac506a918..104f2cb631 100644
--- a/library/inference/branches.factor
+++ b/library/inference/branches.factor
@@ -16,7 +16,7 @@ namespaces parser prettyprint sequences strings vectors words ;
 : unify-values ( seq -- value )
     #! If all values in list are equal, return the value.
     #! Otherwise, unify.
-    dup [ eq? ] monotonic? [ first ] [ <meet> ] ifte ;
+    dup [ eq? ] monotonic? [ first ] [ drop <computed> ] ifte ;
 
 : unify-stacks ( seq -- stack )
     #! Replace differing literals in stacks with unknown
diff --git a/library/inference/dataflow.factor b/library/inference/dataflow.factor
index 3e160e7681..fba29b4ef0 100644
--- a/library/inference/dataflow.factor
+++ b/library/inference/dataflow.factor
@@ -1,7 +1,7 @@
 ! Copyright (C) 2004, 2005 Slava Pestov.
 ! See http://factor.sf.net/license.txt for BSD license.
 IN: inference
-USING: arrays generic hashtables interpreter kernel lists
+USING: arrays generic hashtables interpreter kernel lists math
 namespaces parser sequences words ;
 
 ! Recursive state. An alist, mapping words to labels.
@@ -29,23 +29,6 @@ C: literal ( obj -- value )
 
 M: literal hashcode value-uid hashcode ;
 
-TUPLE: meet values ;
-
-C: meet ( values -- value )
-    <value> over set-delegate [ set-meet-values ] keep ;
-
-M: meet hashcode value-uid hashcode ;
-
-: (flatten-value)
-    dup meet?
-    [ meet-values [ (flatten-value) ] each ] [ dup set ] ifte ;
-
-: flatten-value ( value -- seq )
-    [ (flatten-value) ] make-hash hash-keys ;
-
-: value-refers? ( referee referrer -- ? )
-    2dup eq? [ 2drop t ] [ flatten-value memq? ] ifte ;
-
 ! The dataflow IR is the first of the two intermediate
 ! representations used by Factor. It annotates concatenative
 ! code with stack flow information and types.
@@ -173,8 +156,7 @@ SYMBOL: current-node
         dup node-in-r % node-out-r %
     ] { } make ;
 
-: uses-value? ( value node -- ? )
-    node-values [ value-refers? ] contains-with? ;
+: uses-value? ( value node -- ? ) node-values memq? ;
 
 : outputs-value? ( value node -- ? )
     2dup node-out-d member? >r node-out-r member? r> or ;
@@ -228,53 +210,13 @@ SYMBOL: current-node
 : all-nodes-with? ( obj node quot -- ? | quot: obj node -- ? )
     swap [ with rot ] all-nodes? 2nip ; inline
 
-SYMBOL: substituted
-
-DEFER: subst-value
-
-: subst-meet ( new old meet -- )
-    #! We avoid mutating the same meet more than once, since
-    #! doing so can introduce cycles.
-    dup substituted get memq? [
-        3drop
-    ] [
-        dup substituted get push meet-values subst-value
-    ] ifte ;
-
-: (subst-value) ( new old value -- value )
-    2dup eq? [
-        2drop
-    ] [
-        dup meet? [
-            pick over swap value-refers? [
-                2nip ! don't substitute a meet into itself
-            ] [
-                [ subst-meet ] keep
-            ] ifte
-        ] [
-            2nip
-        ] ifte
-    ] ifte ;
-
-: subst-value ( new old seq -- )
-    pick pick eq? over empty? or
-    [ 3drop ] [ [ >r 2dup r> (subst-value) ] inject 2drop ] ifte ;
-
-: (subst-values) ( newseq oldseq seq -- )
-    #! Mutates seq.
-    -rot [ pick subst-value ] 2each drop ;
+: (subst-values) ( new old node -- )
+    [ node-in-d subst ] 3keep [ node-in-r subst ] 3keep
+    [ node-out-d subst ] 3keep node-out-r subst ;
 
 : subst-values ( new old node -- )
     #! Mutates the node.
-    [
-        { } clone substituted set [
-            3dup node-in-d  (subst-values)
-            3dup node-in-r  (subst-values)
-            3dup node-out-d (subst-values)
-            3dup node-out-r (subst-values)
-            drop
-        ] each-node 2drop
-    ] with-scope ;
+    [ >r 2dup r> (subst-values) ] each-node 2drop ;
 
 : remember-node ( word node -- )
     #! Annotate each node with the fact it was inlined from
diff --git a/library/inference/kill-literals.factor b/library/inference/kill-literals.factor
index f8c7fc01c0..b87a25b6a9 100644
--- a/library/inference/kill-literals.factor
+++ b/library/inference/kill-literals.factor
@@ -5,14 +5,16 @@ USING: arrays generic hashtables inference kernel math
 namespaces sequences ;
 
 : node-union ( node quot -- hash | quot: node -- )
-    [ swap [ swap call ] each-node-with ] make-hash ; inline
+    [
+        swap [ swap call [ dup set ] each ] each-node-with
+    ] make-hash ; inline
 
-GENERIC: literals* ( node -- )
+GENERIC: literals* ( node -- seq )
 
 : literals ( node -- hash )
     [ literals* ] node-union ;
 
-GENERIC: live-values* ( node -- )
+GENERIC: live-values* ( node -- seq )
 
 : live-values ( node -- hash )
     #! All values that are returned or passed to calls.
@@ -38,51 +40,47 @@ M: f returns* drop ;
     [ node-out-r remove-all ] keep set-node-out-r ;
 
 : kill-node ( values node -- )
-    over hash-size 0 > [
-        [ remove-values ] each-node-with
-    ] [
-       2drop
-    ] ifte ;
+    over hash-size 0 >
+    [ [ remove-values ] each-node-with ] [ 2drop ] ifte ;
 
 ! Generic nodes
-M: node literals* ( node -- ) drop ;
+M: node literals* ( node -- ) drop @{ }@ ;
 
-M: node live-values* ( node -- )
-    node-values [ (flatten-value) ] each ;
+M: node live-values* ( node -- ) node-values ;
 
 M: node returns* ( node -- seq ) node-successor returns* ;
 
 ! #shuffle
-: shuffle-literals
-    [ dup literal? [ dup set ] [ drop ] ifte ] each ;
-
-M: #shuffle literals* ( node -- )
-    dup node-out-d shuffle-literals
-    node-out-r shuffle-literals ;
+M: #shuffle literals* ( node -- seq )
+    dup node-out-d swap node-out-r
+    [ [ literal? ] subset ] 2apply append ;
 
 ! #return
 M: #return returns* , ;
 
-M: #return live-values* ( node -- )
+M: #return live-values* ( node -- seq )
     #! Values returned by local labels can be killed.
-    dup node-param [ drop ] [ delegate live-values* ] ifte ;
+    dup node-param [ drop @{ }@ ] [ delegate live-values* ] ifte ;
 
 ! nodes that don't use their input values directly
-UNION: #killable #shuffle #call-label #merge #entry #values ;
+UNION: #killable #shuffle #call-label #merge #values ;
 
-M: #killable live-values* ( node -- ) drop ;
+M: #killable live-values* ( node -- seq ) drop @{ }@ ;
+
+! #entry
+M: #entry live-values* ( node -- seq )
+    #! The live values are those which appear in the in-d but
+    #! not in the out-d. These are literals which are replaced
+    #! by computed values in the solve-recursion step.
+    node-out-d ;
 
 ! branching
 UNION: #branch #ifte #dispatch ;
 
-M: #branch returns* ( node -- )
-    node-children [ returns* ] each ;
+M: #branch returns* ( node -- ) node-children [ returns* ] each ;
 
 M: #branch live-values* ( node -- )
     #! This assumes that the last element of each branch is a
     #! #return node.
-    dup delegate live-values*
-    returns [ node-in-d ] map unify-lengths flip [
-        dup [ eq? ] monotonic?
-        [ drop ] [ [ dup set ] each ] ifte
-    ] each ;
+    dup delegate live-values* >r returns [ node-in-d ] map
+    unify-lengths purge-invariants r> append ;
diff --git a/library/inference/optimizer.factor b/library/inference/optimizer.factor
index c33adc4a06..26a22fbc73 100644
--- a/library/inference/optimizer.factor
+++ b/library/inference/optimizer.factor
@@ -17,7 +17,9 @@ GENERIC: optimize-node* ( node -- node/t )
 DEFER: optimize-node
 
 : optimize-children ( node -- ? )
-    f swap node-children [ optimize-node swap >r or r> ] inject ;
+    f swap [
+        node-children [ optimize-node swap >r or r> ] map
+    ] keep set-node-children ;
 
 : optimize-node ( node -- node ? )
     #! Outputs t if any changes were made.
diff --git a/library/inference/recursive-values.factor b/library/inference/recursive-values.factor
index 0c4e53a027..2ef96d0f59 100644
--- a/library/inference/recursive-values.factor
+++ b/library/inference/recursive-values.factor
@@ -10,22 +10,36 @@ M: node collect-recursion* ( label node -- ) 2drop ;
 M: #call-label collect-recursion* ( label node -- )
     tuck node-param = [ node-in-d , ] [ drop ] ifte ;
 
-: collect-recursion ( label node -- seq )
+: collect-recursion ( #label -- seq )
     #! Collect the input stacks of all #call-label nodes that
     #! call given label.
-    [ [ collect-recursion* ] each-node-with ] { } make ;
+    dup node-param swap
+    [ [ collect-recursion* ] each-node-with ] @{ }@ make ;
 
 GENERIC: solve-recursion*
 
 M: node solve-recursion* ( node -- ) drop ;
 
-: join-values ( calls entry -- new old )
-    add unify-lengths [ unify-stacks ] keep peek ;
+: purge-invariants ( stacks -- seq )
+    #! Output a sequence of values which are not present in the
+    #! same position in each sequence of the stacks sequence.
+    flip [ [ eq? ] monotonic? not ] subset concat ;
+
+: join-values ( calls entry -- new old live )
+    add unify-lengths
+    [ flip [ unify-values ] map ] keep
+    [ peek ] keep
+    purge-invariants ;
+
+: entry-values ( node -- new old live )
+    dup collect-recursion swap node-child node-in-d join-values ;
 
 M: #label solve-recursion* ( node -- )
-    dup node-param over collect-recursion >r
-    node-child dup node-in-d r> swap
-    join-values rot subst-values ;
+    #! #entry node-out-d is abused; its not a stack slice, but
+    #! a set of values.
+    [ entry-values ] keep node-child
+    [ set-node-out-d ] keep
+    node-successor subst-values ;
 
 : solve-recursion ( node -- )
     #! Figure out which values survive inner recursions in
diff --git a/library/io/files.factor b/library/io/files.factor
index 853d8cefa6..84c105681d 100644
--- a/library/io/files.factor
+++ b/library/io/files.factor
@@ -1,7 +1,7 @@
 ! Copyright (C) 2004, 2005 Slava Pestov.
 ! See http://factor.sf.net/license.txt for BSD license.
 IN: io
-USING: kernel lists namespaces sequences strings ;
+USING: hashtables kernel lists namespaces sequences strings ;
 
 ! Words for accessing filesystem meta-data.
 
diff --git a/library/test/collections/hashtables.factor b/library/test/collections/hashtables.factor
index 413e37fb88..65d4eb11dc 100644
--- a/library/test/collections/hashtables.factor
+++ b/library/test/collections/hashtables.factor
@@ -185,3 +185,5 @@ f 100000000000000000000000000 "testhash" get set-hash
     {{ [[ 2 4 ]] [[ 6 5 ]] }} {{ [[ 1 2 ]] [[ 2 3 ]] }}
     hash-union
 ] unit-test
+
+[ [ 1 3 ] ] [ {{ [[ 2 2 ]] }} [ 1 2 3 ] remove-all ] unit-test
diff --git a/library/test/collections/sequences.factor b/library/test/collections/sequences.factor
index 238355ff9c..9f51369cec 100644
--- a/library/test/collections/sequences.factor
+++ b/library/test/collections/sequences.factor
@@ -98,8 +98,6 @@ unit-test
 [ f ] [ 3 [ 1 2 3 ] tail ] unit-test
 [ [ 3 ] ] [ 2 [ 1 2 3 ] tail ] unit-test
 
-[ [ 1 3 ] ] [ [ 2 ] [ 1 2 3 ] remove-all ] unit-test
-
 [ t ] [ [ 1 2 3 ] [ 1 2 3 ] sequence= ] unit-test
 [ t ] [ [ 1 2 3 ] { 1 2 3 } sequence= ] unit-test
 [ t ] [ { 1 2 3 } [ 1 2 3 ] sequence= ] unit-test
@@ -160,3 +158,9 @@ unit-test
 [ { 1 4 9 } ] [ { 1 2 3 } clone dup [ sq ] inject ] unit-test
 
 [ { 3 4 5 } ] [ 2 { 1 2 3 } clone [ [ + ] inject-with ] keep ] unit-test
+
+[ { "one" "two" "three" 4 5 6 } ]
+[
+    { "one" "two" "three" }
+    { 1 2 3 } { 1 2 3 4 5 6 } clone [ subst ] keep
+] unit-test
diff --git a/library/test/compiler/optimizer.factor b/library/test/compiler/optimizer.factor
index 73a02aa4b5..f0114c28c8 100644
--- a/library/test/compiler/optimizer.factor
+++ b/library/test/compiler/optimizer.factor
@@ -1,7 +1,7 @@
 IN: temporary
 USING: arrays assembler compiler compiler-backend generic
-inference kernel kernel-internals lists math optimizer
-prettyprint sequences strings test vectors words ;
+hashtables inference kernel kernel-internals lists math
+optimizer prettyprint sequences strings test vectors words ;
 
 : kill-1
     [ 1 2 3 ] [ + ] over drop drop ; compiled
@@ -33,17 +33,21 @@ prettyprint sequences strings test vectors words ;
 
 [ [ 1 2 3 ] [ 4 5 6 ] [ 1 2 3 ] ] [ kill-6 ] unit-test
 
-: kill-set*
+: subset? swap [ swap member? ] all-with? ;
+
+: set= 2dup subset? >r swap subset? r> and ;
+
+: kill-set=
     dataflow dup solve-recursion dup split-node
-    kill-set [ literal-value ] map ;
+    kill-set hash-keys [ literal-value ] map set= ;
 
 : foo 1 2 3 ;
 
-[ f ] [ \ foo word-def dataflow kill-set ] unit-test
+[ {{ }} ] [ \ foo word-def dataflow kill-set ] unit-test
 
-[ [ [ 1 ] [ 2 ] ] ] [ [ [ 1 ] [ 2 ] ifte ] kill-set* ] unit-test
+[ t ] [ [ [ 1 ] [ 2 ] ] [ [ 1 ] [ 2 ] ifte ] kill-set= ] unit-test
 
-[ [ [ 1 ] [ 2 ] ] ] [ [ [ 1 ] [ 2 ] ifte ] kill-set* ] unit-test
+[ t ] [ [ [ 1 ] [ 2 ] ] [ [ 1 ] [ 2 ] ifte ] kill-set= ] unit-test
 
 : literal-kill-test-1 4 compiled-offset cell 2 * - ; compiled
 
@@ -57,7 +61,7 @@ prettyprint sequences strings test vectors words ;
 
 [ 3 ] [ literal-kill-test-3 ] unit-test
 
-[ [ [ 3 ] [ dup ] 3 ] ] [ [ [ 3 ] [ dup ] ifte drop ] kill-set* ] unit-test
+[ t ] [ [ [ 3 ] [ dup ] 3 ] [ [ 3 ] [ dup ] ifte drop ] kill-set= ] unit-test
 
 : literal-kill-test-4
     5 swap [ 3 ] [ dup ] ifte 2drop ; compiled
@@ -65,14 +69,9 @@ prettyprint sequences strings test vectors words ;
 [ ] [ t literal-kill-test-4 ] unit-test
 [ ] [ f literal-kill-test-4 ] unit-test
 
-: subset? swap [ swap member? ] all-with? ;
-
-: set= 2dup subset? >r swap subset? r> and ;
-
 [ t ] [
     [ 5 [ 3 ] [ dup ] 3 ]
-    \ literal-kill-test-4 word-def kill-set*
-    set=
+    \ literal-kill-test-4 word-def kill-set=
 ] unit-test
 
 : literal-kill-test-5
@@ -83,8 +82,7 @@ prettyprint sequences strings test vectors words ;
 
 [ t ] [
     [ 5 [ 5 ] [ dup ] 5 ]
-    \ literal-kill-test-5 word-def kill-set*
-    set=
+    \ literal-kill-test-5 word-def kill-set=
 ] unit-test
 
 : literal-kill-test-6
@@ -94,7 +92,7 @@ prettyprint sequences strings test vectors words ;
 [ ] [ f literal-kill-test-6 ] unit-test
 
 [ t ] [ [
-    5 [ dup ] [ dup ] ] \ literal-kill-test-6 word-def kill-set* set=
+    5 [ dup ] [ dup ] ] \ literal-kill-test-6 word-def kill-set=
 ] unit-test
 
 : literal-kill-test-7