English
A finitely generated subgroup is finitely generated as an additive subgroup; equivalence with the additive counterpart.
Русский
Конечнопорожденная подгруппа эквивалентна конечнопорожденности как AddSubgroup.
LaTeX
$$$\forall P : Subgroup G, P.FG \iff P.toAddSubgroup.FG$$$
Lean4
theorem fg_iff_add_fg (P : Subgroup G) : P.FG ↔ P.toAddSubgroup.FG :=
by
rw [Subgroup.fg_iff_submonoid_fg, AddSubgroup.fg_iff_addSubmonoid_fg]
exact (Subgroup.toSubmonoid P).fg_iff_add_fg