Theorem: Pos.mul_left_comm (Extra/Pos/Lemmas.lean)

State before:
x y z : Pos
⊢ x * (y * z) = y * (x * z)
Tactic:
by_toNat
State after:
x y z : Pos
⊢ x.toNat * (y.toNat * z.toNat) = y.toNat * (x.toNat * z.toNat)

State before:
x y z : Pos
⊢ x.toNat * (y.toNat * z.toNat) = y.toNat * (x.toNat * z.toNat)
Tactic:
exact Nat.mul_left_comm ..
State after:
no goals