some remaining exercises in Chapter 2 #3245

Job	Run time
nix	2m 22s
opam-build (supported, ubuntu-latest)	5m 11s
quick-build (supported, ubuntu-latest)	3m 21s
opam-build (latest, ubuntu-latest)	5m 4s
build (supported)	3m 24s
quick-build (latest, ubuntu-latest)	3m 15s
opam-build (dev, ubuntu-latest)	7m 12s
build (latest)	3m 22s
quick-build (dev, ubuntu-latest)	3m 15s
build (dev, --warnings)	3m 23s
doc-timing	1m 43s
doc-alectryon	15m 2s
doc-dep-graphs	7m 37s
install (supported)	1m 40s
install (latest)	1m 41s
coqchk (supported)	2m 1s
install (dev)	1m 42s
doc-coqdoc	1m 28s
coqchk (latest)	2m 4s
coqchk (dev)	1m 57s
deploy-doc	0s
delete-artifacts	6s
	1h 16m 50s

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