feat(algebra/homology): i-th component of a chain map as a →+ (#7743)
feat(algebra/homology): i-th component of a chain map as a →+ (#7743)

From LTE.



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

leanprover-community/mathlib,leanprover-community/mathlib