Apply nat_ind to the current goal.
We will prove 0 * 0 = 0.
An exact proof term for the current goal is (mul_nat_0R 0).
Let m be given.
Assume Hm: nat_p m.
Assume IHm: 0 * m = 0.
We will prove 0 * ordsucc m = 0.
rewrite the current goal using (mul_nat_SR 0 m Hm) (from left to right).
We will prove 0 + 0 * m = 0.
rewrite the current goal using IHm (from left to right).
We will prove 0 + 0 = 0.
An exact proof term for the current goal is (add_nat_0R 0).