Theorem: MyRing.add_right_neg (LeanInRome/S2_Basics/S02_Proving_Identities_in_Algebraic_Structures.lean)

State before:
R : Type u_1
inst✝ : Ring R
a : R
⊢ a + -a = 0
Tactic:
rw [add_comm, add_left_neg]
State after:
no goals