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

State before:
R : Type u_1
inst✝ : Ring R
a b : R
⊢ a + b + -b = a
Tactic:
rw [add_assoc, add_right_neg, add_zero]
State after:
no goals