Commit 2020-09-11 14:46 bd74baa1

feat(algebra/homology/exact): lemmas about exactness (#4106) These are a few lemmas on the way to showing how exact changes under isomorphisms applied to the objects. It's not everthing one might want; I'm salvaging this from an old branch and unlikely to do more in the near future, but hopefully this is mergeable progress as is.