diff --git a/core/sequences/sequences-docs.factor b/core/sequences/sequences-docs.factor
index 81c50de976..a4696a76ae 100755
--- a/core/sequences/sequences-docs.factor
+++ b/core/sequences/sequences-docs.factor
@@ -64,8 +64,7 @@ ARTICLE: "sequences-add-remove" "Adding and removing sequence elements"
 { $subsection prefix }
 { $subsection suffix }
 "Removing elements:"
-{ $subsection remove }
-{ $subsection diff } ;
+{ $subsection remove } ;
 
 ARTICLE: "sequences-reshape" "Reshaping sequences"
 "A " { $emphasis "repetition" } " is a virtual sequence consisting of a single element repeated multiple times:"
diff --git a/core/sets/sets-docs.factor b/core/sets/sets-docs.factor
index f7df9a5593..01b8b8efd7 100644
--- a/core/sets/sets-docs.factor
+++ b/core/sets/sets-docs.factor
@@ -54,3 +54,5 @@ HELP: union
 { $examples
     { $example "USING: sequences prettyprint ;" "{ 1 2 3 } { 2 3 4 } union ." "{ 1 2 3 4 }" }
 } ;
+
+{ diff intersect union } related-words
diff --git a/extra/contributors/contributors.factor b/extra/contributors/contributors.factor
index d0da724cc6..868e968169 100755
--- a/extra/contributors/contributors.factor
+++ b/extra/contributors/contributors.factor
@@ -1,7 +1,8 @@
 ! Copyright (C) 2007 Slava Pestov.
 ! See http://factorcode.org/license.txt for BSD license.
 USING: io.files io.launcher io.styles io hashtables kernel
-sequences sequences.lib assocs system sorting math.parser ;
+sequences sequences.lib assocs system sorting math.parser
+sets ;
 IN: contributors
 
 : changelog ( -- authors )
diff --git a/extra/help/lint/lint.factor b/extra/help/lint/lint.factor
index 01e08473c6..28af93f295 100755
--- a/extra/help/lint/lint.factor
+++ b/extra/help/lint/lint.factor
@@ -5,7 +5,7 @@ words strings classes tools.vocabs namespaces io
 io.streams.string prettyprint definitions arrays vectors
 combinators splitting debugger hashtables sorting effects vocabs
 vocabs.loader assocs editors continuations classes.predicate
-macros combinators.lib sequences.lib math ;
+macros combinators.lib sequences.lib math sets ;
 IN: help.lint
 
 : check-example ( element -- )
diff --git a/extra/io/unix/kqueue/kqueue.factor b/extra/io/unix/kqueue/kqueue.factor
index 3a140bdbec..3e3ac18dd6 100644
--- a/extra/io/unix/kqueue/kqueue.factor
+++ b/extra/io/unix/kqueue/kqueue.factor
@@ -2,7 +2,7 @@
 ! See http://factorcode.org/license.txt for BSD license.
 USING: alien.c-types kernel math math.bitfields namespaces
 locals accessors combinators threads vectors hashtables
-sequences assocs continuations
+sequences assocs continuations sets
 unix unix.time unix.kqueue unix.process
 io.nonblocking io.unix.backend io.launcher io.unix.launcher
 io.monitors ;
diff --git a/extra/io/unix/linux/monitors/monitors.factor b/extra/io/unix/linux/monitors/monitors.factor
index f92fb36d0d..ee36fc82d1 100644
--- a/extra/io/unix/linux/monitors/monitors.factor
+++ b/extra/io/unix/linux/monitors/monitors.factor
@@ -3,7 +3,7 @@
 USING: kernel io.backend io.monitors io.monitors.recursive
 io.files io.buffers io.monitors io.nonblocking io.timeouts
 io.unix.backend io.unix.select unix.linux.inotify assocs
-namespaces threads continuations init math math.bitfields
+namespaces threads continuations init math math.bitfields sets
 alien.c-types alien vocabs.loader accessors system hashtables ;
 IN: io.unix.linux.monitors
 
diff --git a/extra/koszul/koszul.factor b/extra/koszul/koszul.factor
index e3c2997d0b..b079cec42c 100755
--- a/extra/koszul/koszul.factor
+++ b/extra/koszul/koszul.factor
@@ -3,7 +3,7 @@
 USING: arrays assocs hashtables assocs io kernel math
 math.vectors math.matrices math.matrices.elimination namespaces
 parser prettyprint sequences words combinators math.parser
-splitting sorting shuffle symbols ;
+splitting sorting shuffle symbols sets ;
 IN: koszul
 
 ! Utilities
diff --git a/extra/locals/locals.factor b/extra/locals/locals.factor
index a936d8c1ee..2b0c61cc89 100755
--- a/extra/locals/locals.factor
+++ b/extra/locals/locals.factor
@@ -3,7 +3,7 @@
 USING: kernel namespaces sequences sequences.private assocs math
 inference.transforms parser words quotations debugger macros
 arrays macros splitting combinators prettyprint.backend
-definitions prettyprint hashtables prettyprint.sections
+definitions prettyprint hashtables prettyprint.sections sets
 sequences.private effects generic compiler.units accessors ;
 IN: locals
 
diff --git a/extra/math/miller-rabin/miller-rabin.factor b/extra/math/miller-rabin/miller-rabin.factor
index c8a21512ec..7835277b9b 100755
--- a/extra/math/miller-rabin/miller-rabin.factor
+++ b/extra/math/miller-rabin/miller-rabin.factor
@@ -1,6 +1,6 @@
 USING: combinators combinators.lib io locals kernel math
 math.functions math.ranges namespaces random sequences
-hashtables ;
+hashtables sets ;
 IN: math.miller-rabin
 
 SYMBOL: a
diff --git a/extra/opengl/capabilities/capabilities.factor b/extra/opengl/capabilities/capabilities.factor
index c3a40cc23e..6802d15378 100755
--- a/extra/opengl/capabilities/capabilities.factor
+++ b/extra/opengl/capabilities/capabilities.factor
@@ -1,7 +1,7 @@
 ! Copyright (C) 2008 Joe Groff.
 ! See http://factorcode.org/license.txt for BSD license.
 USING: kernel namespaces sequences splitting opengl.gl
-continuations math.parser math arrays ;
+continuations math.parser math arrays sets ;
 IN: opengl.capabilities
 
 : (require-gl) ( thing require-quot make-error-quot -- )
diff --git a/extra/project-euler/004/004.factor b/extra/project-euler/004/004.factor
index 828c0c3fd8..b2146b4aea 100644
--- a/extra/project-euler/004/004.factor
+++ b/extra/project-euler/004/004.factor
@@ -1,7 +1,7 @@
 ! Copyright (c) 2007 Aaron Schaefer, Daniel Ehrenberg.
 ! See http://factorcode.org/license.txt for BSD license.
 USING: hashtables kernel math math.ranges project-euler.common sequences
-    sorting ;
+    sorting sets ;
 IN: project-euler.004
 
 ! http://projecteuler.net/index.php?section=problems&id=4
diff --git a/extra/project-euler/023/023.factor b/extra/project-euler/023/023.factor
index 1219af1f15..1dd7878a3b 100644
--- a/extra/project-euler/023/023.factor
+++ b/extra/project-euler/023/023.factor
@@ -1,7 +1,7 @@
 ! Copyright (c) 2008 Aaron Schaefer.
 ! See http://factorcode.org/license.txt for BSD license.
 USING: hashtables kernel math math.ranges project-euler.common sequences
-    sorting ;
+    sorting sets ;
 IN: project-euler.023
 
 ! http://projecteuler.net/index.php?section=problems&id=23
diff --git a/extra/project-euler/029/029.factor b/extra/project-euler/029/029.factor
index 459a3a4bd6..9cfe0aacff 100644
--- a/extra/project-euler/029/029.factor
+++ b/extra/project-euler/029/029.factor
@@ -1,7 +1,7 @@
 ! Copyright (c) 2008 Aaron Schaefer.
 ! See http://factorcode.org/license.txt for BSD license.
 USING: hashtables kernel math.functions math.ranges project-euler.common
-    sequences ;
+    sequences sets ;
 IN: project-euler.029
 
 ! http://projecteuler.net/index.php?section=problems&id=29
diff --git a/extra/project-euler/032/032.factor b/extra/project-euler/032/032.factor
index 0981c68e1c..7b24004df6 100755
--- a/extra/project-euler/032/032.factor
+++ b/extra/project-euler/032/032.factor
@@ -1,7 +1,7 @@
 ! Copyright (c) 2008 Aaron Schaefer.
 ! See http://factorcode.org/license.txt for BSD license.
 USING: combinators.lib hashtables kernel math math.combinatorics math.functions
-    math.parser math.ranges project-euler.common sequences ;
+    math.parser math.ranges project-euler.common sequences sets ;
 IN: project-euler.032
 
 ! http://projecteuler.net/index.php?section=problems&id=32
diff --git a/extra/project-euler/035/035.factor b/extra/project-euler/035/035.factor
index 63b80b6d63..c362e1e1a5 100755
--- a/extra/project-euler/035/035.factor
+++ b/extra/project-euler/035/035.factor
@@ -1,7 +1,7 @@
 ! Copyright (c) 2008 Aaron Schaefer.
 ! See http://factorcode.org/license.txt for BSD license.
 USING: kernel math math.combinatorics math.parser math.primes
-    project-euler.common sequences sequences.lib ;
+    project-euler.common sequences sequences.lib sets ;
 IN: project-euler.035
 
 ! http://projecteuler.net/index.php?section=problems&id=35
diff --git a/extra/project-euler/043/043.factor b/extra/project-euler/043/043.factor
index 37963d6bd3..0d1eb00bfa 100644
--- a/extra/project-euler/043/043.factor
+++ b/extra/project-euler/043/043.factor
@@ -1,7 +1,7 @@
 ! Copyright (c) 2008 Aaron Schaefer.
 ! See http://factorcode.org/license.txt for BSD license.
 USING: combinators.lib hashtables kernel math math.combinatorics math.parser
-    math.ranges project-euler.common sequences sequences.lib sorting ;
+    math.ranges project-euler.common sequences sequences.lib sorting sets ;
 IN: project-euler.043
 
 ! http://projecteuler.net/index.php?section=problems&id=43
diff --git a/extra/project-euler/059/059.factor b/extra/project-euler/059/059.factor
index 1c20d1ab34..bb95ab9024 100644
--- a/extra/project-euler/059/059.factor
+++ b/extra/project-euler/059/059.factor
@@ -2,7 +2,7 @@
 ! See http://factorcode.org/license.txt for BSD license.
 USING: arrays ascii assocs hashtables io.encodings.ascii io.files kernel math
     math.parser namespaces sequences sequences.lib sequences.private sorting
-    splitting strings ;
+    splitting strings sets ;
 IN: project-euler.059
 
 ! http://projecteuler.net/index.php?section=problems&id=59
diff --git a/extra/project-euler/079/079.factor b/extra/project-euler/079/079.factor
index 6f9191234b..452a64af44 100644
--- a/extra/project-euler/079/079.factor
+++ b/extra/project-euler/079/079.factor
@@ -1,7 +1,7 @@
 ! Copyright (c) 2008 Aaron Schaefer.
 ! See http://factorcode.org/license.txt for BSD license.
 USING: assocs hashtables io.files kernel math math.parser namespaces
-io.encodings.ascii sequences ;
+io.encodings.ascii sequences sets ;
 IN: project-euler.079
 
 ! http://projecteuler.net/index.php?section=problems&id=79
diff --git a/extra/qualified/qualified.factor b/extra/qualified/qualified.factor
index c10a102c58..730388ade0 100644
--- a/extra/qualified/qualified.factor
+++ b/extra/qualified/qualified.factor
@@ -1,5 +1,5 @@
 USING: kernel sequences assocs hashtables parser vocabs words namespaces
-vocabs.loader debugger ;
+vocabs.loader debugger sets ;
 IN: qualified
 
 : define-qualified ( vocab-name prefix-name -- )
diff --git a/extra/semantic-db/hierarchy/hierarchy.factor b/extra/semantic-db/hierarchy/hierarchy.factor
index 69c7baba9f..0b2421c757 100755
--- a/extra/semantic-db/hierarchy/hierarchy.factor
+++ b/extra/semantic-db/hierarchy/hierarchy.factor
@@ -1,6 +1,6 @@
 ! Copyright (C) 2008 Alex Chapman
 ! See http://factorcode.org/license.txt for BSD license.
-USING: accessors db.tuples hashtables kernel
+USING: accessors db.tuples hashtables kernel sets
 semantic-db semantic-db.relations sequences sequences.deep ;
 IN: semantic-db.hierarchy
 
diff --git a/extra/tools/vocabs/vocabs.factor b/extra/tools/vocabs/vocabs.factor
index 46936af92c..40e79ee014 100755
--- a/extra/tools/vocabs/vocabs.factor
+++ b/extra/tools/vocabs/vocabs.factor
@@ -3,7 +3,8 @@
 USING: io.files kernel io.encodings.utf8 vocabs.loader vocabs
 sequences namespaces math.parser arrays hashtables assocs
 memoize inspector sorting splitting combinators source-files
-io debugger continuations compiler.errors init io.crc32 ;
+io debugger continuations compiler.errors init io.crc32 
+sets ;
 IN: tools.vocabs
 
 : vocab-tests-file ( vocab -- path )
diff --git a/extra/ui/gadgets/gadgets-tests.factor b/extra/ui/gadgets/gadgets-tests.factor
index fc9ce82f8c..dbe06ec8cd 100755
--- a/extra/ui/gadgets/gadgets-tests.factor
+++ b/extra/ui/gadgets/gadgets-tests.factor
@@ -1,6 +1,6 @@
 IN: ui.gadgets.tests
 USING: ui.gadgets ui.gadgets.packs ui.gadgets.worlds tools.test
-namespaces models kernel dlists math
+namespaces models kernel dlists math sets
 math.parser ui sequences hashtables assocs io arrays
 prettyprint io.streams.string ;
 
diff --git a/extra/ui/gestures/gestures.factor b/extra/ui/gestures/gestures.factor
index 5472af5946..f68a70c2bd 100755
--- a/extra/ui/gestures/gestures.factor
+++ b/extra/ui/gestures/gestures.factor
@@ -3,7 +3,7 @@
 USING: arrays assocs kernel math models namespaces
 sequences words strings system hashtables math.parser
 math.vectors classes.tuple classes ui.gadgets boxes
-calendar alarms symbols combinators ;
+calendar alarms symbols combinators sets ;
 IN: ui.gestures
 
 : set-gestures ( class hash -- ) "gestures" set-word-prop ;
diff --git a/extra/ui/ui.factor b/extra/ui/ui.factor
index 6286297f68..946fe283aa 100755
--- a/extra/ui/ui.factor
+++ b/extra/ui/ui.factor
@@ -4,7 +4,7 @@ USING: arrays assocs io kernel math models namespaces
 prettyprint dlists sequences threads sequences words
 debugger ui.gadgets ui.gadgets.worlds ui.gadgets.tracks
 ui.gestures ui.backend ui.render continuations init combinators
-hashtables concurrency.flags ;
+hashtables concurrency.flags sets ;
 IN: ui
 
 ! Assoc mapping aliens to gadgets
diff --git a/extra/xml/tokenize/tokenize.factor b/extra/xml/tokenize/tokenize.factor
index de6ffed06b..5ba151c213 100644
--- a/extra/xml/tokenize/tokenize.factor
+++ b/extra/xml/tokenize/tokenize.factor
@@ -1,6 +1,6 @@
 ! Copyright (C) 2005, 2006 Daniel Ehrenberg
 ! See http://factorcode.org/license.txt for BSD license.
-USING: xml.errors xml.data xml.utilities xml.char-classes
+USING: xml.errors xml.data xml.utilities xml.char-classes sets
 xml.entities kernel state-parser kernel namespaces strings math
 math.parser sequences assocs arrays splitting combinators unicode.case ;
 IN: xml.tokenize
diff --git a/extra/xmode/keyword-map/keyword-map.factor b/extra/xmode/keyword-map/keyword-map.factor
index 4e97e597b2..a6ef34a1f9 100644
--- a/extra/xmode/keyword-map/keyword-map.factor
+++ b/extra/xmode/keyword-map/keyword-map.factor
@@ -1,5 +1,5 @@
 USING: kernel strings assocs sequences hashtables sorting
-       unicode.case unicode.categories ;
+       unicode.case unicode.categories sets ;
 IN: xmode.keyword-map
 
 ! Based on org.gjt.sp.jedit.syntax.KeywordMap