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

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

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