πₙ(Sⁿ) = Z, and other cleanups #1699

Job	Run time
opam-build (supported, ubuntu-latest)	4m 23s
opam-build (8.17, ubuntu-latest)	4m 19s
quick-build (supported, ubuntu-latest)	2m 38s
build (supported)	2m 58s
opam-build (latest, ubuntu-latest)	4m 16s
quick-build (latest, ubuntu-latest)	2m 39s
nix	2m 15s
build (latest)	2m 50s
opam-build (dev, ubuntu-latest)	4m 25s
quick-build (dev, ubuntu-latest)	2m 43s
build (dev, --warnings)	3m 16s
doc-dep-graphs	7m 5s
doc-timing	1m 3s
doc-coqdoc	59s
coqchk (supported)	1m 25s
doc-alectryon	13m 5s
coqchk (latest)	1m 21s
install (supported)	1m 0s
coqchk (dev)	1m 33s
install (latest)	1m 1s
install (dev)	1m 1s
deploy-doc	0s
delete-artifacts	3s
	1h 6m 18s

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