diff --git a/GNUmakefile b/GNUmakefile
new file mode 100644
index 0000000..ff11fb2
--- /dev/null
+++ b/GNUmakefile
@@ -0,0 +1,198 @@
+VERSION ?= 2021.4
+KEYPAIR ?= 2021-04
+PREFIX ?= /usr/local
+DATADIR ?= $(PREFIX)/share/RETRO12
+DOCSDIR ?= $(PREFIX)/share/doc/RETRO12
+EXAMPLESDIR ?= $(PREFIX)/share/examples/RETRO12
+MANDIR ?= $(PREFIX)/share/man/man1
+LIBM ?= -lm
+
+all: build
+
+help:
+
+build: dirs toolchain ngaImage bin/retro bin/retro-describe
+
+optional: build bin/retro-repl
+
+toolchain: dirs bin/retro-embedimage bin/retro-extend bin/retro-muri bin/retro-unu
+
+image: vm/nga-c/image.c
+
+repl: bin/retro-repl
+
+dirs:
+	mkdir -p bin
+	cp tools/retro-document.sh bin/retro-document
+
+clean:
+	rm -f bin/*
+
+
+# installation targets
+
+install: build install-data install-docs install-examples install-manpages
+	install -m 755 -d -- $(DESTDIR)$(PREFIX)/bin
+	install -c -m 755 bin/retro-embedimage $(DESTDIR)$(PREFIX)/bin/retro-embedimage
+	install -c -m 755 bin/retro-extend $(DESTDIR)$(PREFIX)/bin/retro-extend
+	install -c -m 755 bin/retro-muri $(DESTDIR)$(PREFIX)/bin/retro-muri
+	install -c -m 755 bin/retro $(DESTDIR)$(PREFIX)/bin/retro
+	install -c -m 755 bin/retro-unu $(DESTDIR)$(PREFIX)/bin/retro-unu
+	install -c -m 755 bin/retro-describe $(DESTDIR)$(PREFIX)/bin/retro-describe
+	install -c -m 755 bin/retro-document $(DESTDIR)$(PREFIX)/bin/retro-document
+	install -c -m 755 example/retro-tags.retro $(DESTDIR)$(PREFIX)/bin/retro-tags
+	install -c -m 755 example/retro-locate.retro $(DESTDIR)$(PREFIX)/bin/retro-locate
+
+install-strip: build install-data install-docs install-examples
+	install -m 755 -d -- $(DESTDIR)/bin
+	install -c -m 755 -s bin/retro-embedimage $(DESTDIR)$(PREFIX)/bin/retro-embedimage
+	install -c -m 755 -s bin/retro-extend $(DESTDIR)$(PREFIX)/bin/retro-extend
+	install -c -m 755 -s bin/retro-muri $(DESTDIR)$(PREFIX)/bin/retro-muri
+	install -c -m 755 -s bin/retro $(DESTDIR)$(PREFIX)/bin/retro
+	install -c -m 755 -s bin/retro-unu $(DESTDIR)$(PREFIX)/bin/retro-unu
+	install -c -m 755 bin/retro-describe $(DESTDIR)$(PREFIX)/bin/retro-describe
+	install -c -m 755 bin/retro-document $(DESTDIR)$(PREFIX)/bin/retro-document
+	install -c -m 755 example/retro-tags.retro $(DESTDIR)$(PREFIX)/bin/retro-tags
+	install -c -m 755 example/retro-locate.retro $(DESTDIR)$(PREFIX)/bin/retro-locate
+
+install-data:
+	install -m 755 -d -- $(DESTDIR)$(DATADIR)
+	install -c -m 644 tools/glossary.retro $(DESTDIR)$(DATADIR)/glossary.retro
+	install -c -m 644 ngaImage $(DESTDIR)$(DATADIR)/ngaImage
+	cp -fpR tests $(DESTDIR)$(DATADIR)/
+	install -c -m 644 doc/words.tsv $(DESTDIR)$(DATADIR)/words.tsv
+
+install-docs:
+	install -m 755 -d -- $(DESTDIR)$(DOCSDIR)
+	install -c -m 644 README $(DESTDIR)$(DOCSDIR)/README
+	install -c -m 644 RELEASE-NOTES $(DESTDIR)$(DOCSDIR)/RELEASE-NOTES
+	install -c -m 644 doc/RETRO-Book.md $(DESTDIR)$(DOCSDIR)/RETRO-Book.md
+	install -c -m 644 doc/words.tsv $(DESTDIR)$(DOCSDIR)/words.tsv
+
+install-examples:
+	install -m 755 -d -- $(DESTDIR)$(EXAMPLESDIR)
+	cp -fpR example $(DESTDIR)$(EXAMPLESDIR)
+
+install-manpages:
+	install -m 755 -d -- $(DESTDIR)$(MANDIR)
+	install -c -m 644 man/retro.1 $(DESTDIR)$(MANDIR)/retro.1
+	install -c -m 644 man/retro-embedimage.1 $(DESTDIR)$(MANDIR)/retro-embedimage.1
+	install -c -m 644 man/retro-extend.1 $(DESTDIR)$(MANDIR)/retro-extend.1
+	install -c -m 644 man/retro-describe.1 $(DESTDIR)$(MANDIR)/retro-describe.1
+	install -c -m 644 man/retro-document.1 $(DESTDIR)$(MANDIR)/retro-document.1
+	install -c -m 644 man/retro-muri.1 $(DESTDIR)$(MANDIR)/retro-muri.1
+	install -c -m 644 man/retro-unu.1 $(DESTDIR)$(MANDIR)/retro-unu.1
+	install -c -m 644 man/retro-tags.1 $(DESTDIR)$(MANDIR)/retro-tags.1
+	install -c -m 644 man/retro-locate.1 $(DESTDIR)$(MANDIR)/retro-locate.1
+
+
+
+# toolchain targets
+
+bin/retro-describe: tools/retro-describe.retro doc/words.tsv
+	cat tools/retro-describe.retro doc/words.tsv >bin/retro-describe
+	chmod +x bin/retro-describe
+
+bin/retro-embedimage: tools/retro-embedimage.c
+	$(CC) $(OPTIONS) $(CFLAGS) $(LDFLAGS) -o $@ tools/retro-embedimage.c
+
+bin/retro-extend: tools/retro-extend.c
+	$(CC) $(OPTIONS) $(CFLAGS) $(LDFLAGS) -o $@  tools/retro-extend.c
+
+bin/retro-muri: tools/retro-muri.c
+	$(CC) $(OPTIONS) $(CFLAGS) $(LDFLAGS) -o $@ tools/retro-muri.c
+
+bin/retro-unu: tools/retro-unu.c
+	$(CC) $(OPTIONS) $(CFLAGS) $(LDFLAGS) -o $@ tools/retro-unu.c
+
+
+
+# basic image target
+
+ngaImage: image/retro.muri image/retro.forth bin/retro-muri bin/retro-extend
+	./bin/retro-muri image/retro.muri
+	./bin/retro-extend ngaImage image/retro.forth
+
+
+
+# minimal system
+
+bin/retro-repl: vm/nga-c/repl.c vm/nga-c/image.c
+	cd vm/nga-c && $(CC) $(OPTIONS) $(CFLAGS) $(LDFLAGS) -o ../../bin/retro-repl repl.c
+
+
+
+# retro on unix
+
+update-extensions: bin/retro
+	cd package/extensions && ../../bin/retro -f ../../tools/generate-extensions-list.retro >../load-extensions.retro
+
+vm/nga-c/retro-image.c: ngaImage bin/retro-embedimage bin/retro-extend interface/filesystem.retro interface/floatingpoint.retro interface/unix.retro interface/rng.retro interface/sockets.retro interface/scripting.retro interface/retro-unix.retro interface/clock.retro
+	cp ngaImage rre.image
+	./bin/retro-extend rre.image interface/filesystem.retro interface/floatingpoint.retro interface/unix.retro interface/rng.retro interface/sockets.retro interface/scripting.retro interface/clock.retro interface/retro-unix.retro 
+	./bin/retro-embedimage rre.image >vm/nga-c/retro-image.c
+
+bin/retro: vm/nga-c/retro-image.c vm/nga-c/retro-unix.c vm/nga-c/bsd-strl.c vm/nga-c/config.h vm/nga-c/dev-clock.c vm/nga-c/dev-files.c vm/nga-c/dev-floatingpoint.c vm/nga-c/dev-image.c vm/nga-c/dev-rng.c vm/nga-c/dev-sockets.c vm/nga-c/dev-unix.c vm/nga-c/prototypes.h package/list.forth package/load-extensions.retro
+	cd vm/nga-c && $(CC) $(OPTIONS) $(CFLAGS) $(LDFLAGS) -o ../../bin/retro retro-unix.c $(LIBM)
+	cd package && ../bin/retro -u rre.image -f list.forth
+	./bin/retro-embedimage rre.image >vm/nga-c/retro-image.c
+	rm rre.image
+	cd vm/nga-c && $(CC) $(OPTIONS) $(CFLAGS) $(LDFLAGS) -o ../../bin/retro retro-unix.c $(LIBM)
+
+
+
+# optional targets
+
+bin/retro-compiler: bin/retro-extend vm/nga-c/retro-compiler.c vm/nga-c/retro-runtime.c vm/nga-c/bsd-strl.c vm/nga-c/config.h vm/nga-c/dev-clock.c vm/nga-c/dev-files.c vm/nga-c/dev-floatingpoint.c vm/nga-c/dev-image.c vm/nga-c/dev-rng.c vm/nga-c/dev-sockets.c vm/nga-c/dev-unix.c vm/nga-c/prototypes.h
+	cp ngaImage runtime.image
+	./bin/retro-extend runtime.image interface/scripting.retro interface/filesystem.retro interface/floatingpoint.retro interface/unix.retro interface/rng.retro interface/retro-unix.retro interface/clock.retro
+	cd vm/nga-c && $(CC) $(OPTIONS) $(CFLAGS) $(LDFLAGS) -o ../../retro-runtime retro-runtime.c $(LIBM)
+	cd vm/nga-c && $(CC) $(OPTIONS) $(CFLAGS) $(LDFLAGS) -o ../../bin/retro-compiler retro-compiler.c
+	objcopy --add-section .ngaImage=runtime.image --set-section-flags .ngaImage=noload,readonly bin/retro-compiler
+	objcopy --add-section .runtime=retro-runtime --set-section-flags .runtime=noload,readonly bin/retro-compiler
+	rm runtime.image retro-runtime
+
+image-js: bin/retro
+	./bin/retro example/retro-generate-image-js.retro >vm/nga-js/image.js
+
+
+
+# documentation targets
+
+glossary: doc/Glossary.txt doc/Glossary.html doc/Glossary-Concise.txt doc/Glossary-Names-and-Stack.txt doc/words.tsv
+
+sorted: doc/words.tsv
+	LC_ALL=C sort -o sorted.tsv doc/words.tsv
+	mv sorted.tsv doc/words.tsv
+
+doc/Glossary.txt: bin/retro sorted
+	./bin/retro tools/glossary.retro export glossary >doc/Glossary.txt
+
+doc/Glossary.html: bin/retro sorted
+	./bin/retro tools/glossary.retro export html >doc/Glossary.html
+
+doc/Glossary-Concise.txt: bin/retro sorted
+	./bin/retro tools/glossary.retro export concise >doc/Glossary-Concise.txt
+
+doc/Glossary-Names-and-Stack.txt: bin/retro sorted
+	./bin/retro tools/glossary.retro export concise-stack >doc/Glossary-Names-and-Stack.txt
+
+
+
+# other targets
+
+release: clean build glossary
+	fossil tarball tip R12.tar.gz
+	mkdir release
+	cd release && tar xzvf ../R12.tar.gz
+	cd release && mv * RETRO12-$(VERSION)
+	cd release && tar cf RETRO12-$(VERSION).tar RETRO12-$(VERSION)
+	cd release && gzip RETRO12-$(VERSION).tar
+	mv release/RETRO12-$(VERSION).tar.gz .
+	rm -rf release
+	signify -S -s /home/crc/keys/$(KEYPAIR).sec -m RETRO12-$(VERSION).tar.gz
+	signify -V -p security/$(KEYPAIR).pub -m RETRO12-$(VERSION).tar.gz
+
+test: bin/retro
+	./bin/retro tests/test-core.forth
+
diff --git a/vm/nga-c-native-x86/image.c b/vm/nga-c-native-x86/image.c
index dcc07ed..81db113 100644
--- a/vm/nga-c-native-x86/image.c
+++ b/vm/nga-c-native-x86/image.c
@@ -3,7 +3,7 @@
 #define CELL int32_t
 #endif
 CELL ngaImageCells = 13846;
-CELL ngaImage[] = { 1793,13757,13747,13845,202102,0,10,1,10,2,10,3,10,4,10,5,10,6,10,
+CELL ngaImage[] = { 1793,13757,13747,13845,202104,0,10,1,10,2,10,3,10,4,10,5,10,6,10,
                        7,10,8,10,9,10,10,11,10,12,10,13,10,14,10,15,10,16,10,17,
                        10,18,10,19,10,20,10,21,10,22,10,23,10,24,10,25,10,68223234,1,2575,
                        85000450,1,656912,3211,3220,268505089,63,62,285281281,0,63,2063,10,101384453,0,9,10,2049,56,25,