Add proof that map is injective (#2061) #998

Job	Run time
install (8.20.0, Ubuntu, ubuntu-latest, 4.09.1)	40m 22s
install (8.20.0, Windows, windows-latest, 4.13.1, -async-proofs-j 1, git+https://github.com/ocaml...	1h 36m 15s
install (8.18.0, Ubuntu, ubuntu-latest, 4.09.1)	42m 28s
install (8.18.0, Windows, windows-latest, 4.13.1, -async-proofs-j 1, git+https://github.com/ocaml...	1h 39m 48s
install (dev, Windows, windows-latest, 4.13.1, -async-proofs-j 1, git+https://github.com/ocaml/oc...	1h 31m 0s
install (8.20.0, macOS, macos-latest, 4.14.2)	36m 43s
install (8.19.0, Windows, windows-latest, 4.13.1, -async-proofs-j 1, git+https://github.com/ocaml...	1h 35m 33s
install (dev, Ubuntu, ubuntu-latest, 4.09.1)	40m 17s
install (dev, macOS, macos-latest, 4.14.2)	37m 1s
install (8.18.0, macOS, macos-latest, 4.14.2)	41m 42s
install (8.19.0, macOS, macos-latest, 4.14.2)	43m 6s
install (8.19.0, Ubuntu, ubuntu-latest, 4.09.1)	40m 8s
	11h 44m 23s

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