simp only [← coe_inj, hs, coe_mul, coe_mulStab, ← stabilizer_coe_finset, stabilizer_mul_self]
case inr
ι : Type u_1
α : Type u_2
inst✝¹ : Group α
inst✝ : DecidableEq α
s✝ t : Finset α
a : α
s : Finset α
hs : s.Nonempty
⊢ s.mulStab * s = s
no goals