Theorem: MyRing.add_left_cancel (LeanInRome/S2_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:
sorry
State after:
no goals