Theorem: MyRing.add_left_cancelαα (MIL/C02_Basics/S02_Proving_Identities_in_Algebraic_Structures.lean)

State before:
R : Type u_1
inst✝ : Ring R
a b c : R
h : a + b = a + c
⊢ b = c
Tactic:
rw [← neg_add_cancel_left a b, h, neg_add_cancel_left]
State after:
no goals