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

State before:
x y z : Pos
⊢ x + y = x + z → y = z
Tactic:
by_toNat
State after:
x y z : Pos
⊢ x.toNat + y.toNat = x.toNat + z.toNat → y.toNat = z.toNat

State before:
x y z : Pos
⊢ x.toNat + y.toNat = x.toNat + z.toNat → y.toNat = z.toNat
Tactic:
exact Nat.add_left_cancel
State after:
no goals