English
An extensional lemma for CommGrpCat: equality of morphisms follows from equality of their underlying Hom components.
Русский
Лемма экстенсионности для CommGrpCat: равенство морфизмов следует из равенства их базовых компонентов hом.
LaTeX
$$$ \\forall \\; f,g:\\, X \\to Y,\\; f.hom = g.hom \\Rightarrow f = g $$$
Lean4
@[to_additive]
-- This is not `simp` to avoid rewriting in types of terms.
theorem coe_of (R : Type u) [CommGroup R] : ↑(CommGrpCat.of R) = R :=
rfl