mathlib

893c4746 - feat(group_theory/submonoid/membership): add log, exp lemmas (#8870)

feat(group_theory/submonoid/membership): add log, exp lemmas (#8870) Breaking up a previous PR (#7843) into smaller ones. This PR adds lemmas about injectivity of `pow` and `log` functions under appropriate conditions. [Zulip](https://leanprover.zulipchat.com/#narrow/stream/144837-PR-reviews/topic/.238870)