feat(algebra/category/Module): the monoidal category of R-modules is symmetric (#4140)
feat(algebra/category/Module): the monoidal category of R-modules is symmetric (#4140)





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

leanprover-community/mathlib,leanprover-community/mathlib