feat(set_theory/ordinal_arithmetic): `enum_ord univ = id` (#12391)
feat(set_theory/ordinal_arithmetic): `enum_ord univ = id` (#12391)




Co-authored-by: Johan Commelin <759412786bc533369b22377bf83fb9056c5b25b2@commelin.net>

leanprover-community/mathlib,leanprover-community/mathlib