mathlib4
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Feat(Algebra/Regular/SMul): Add some lemmas about `IsSMulRegular`
Add some lemmas about IsSMulRegular.
I'm not sure if it's okay to add the Mathlib.GroupTheory.GroupAction.Hom import. My understanding is that this file is kept low in the hierarchy for some reason, but I'm not sure what that reason is or if this pushes it too far ahead. I added it for access to MulActionHomClass in isSMulRegular_of_injective_of_isSMulRegular.