feat(category_theory/kernels): compute kernel (f ≫ g) when one is an iso (#3438)
feat(category_theory/kernels): compute kernel (f ≫ g) when one is an iso (#3438)



Co-authored-by: Scott Morrison <63f04b4d96235eb042cc46d94f14d241d2a26722@gmail.com>

leanprover-community/mathlib,leanprover-community/mathlib