Let x and y be given.

Assume Hx Hy.

rewrite the current goal using mul_SNo_minus_distrL x (- y) Hx (SNo_minus_SNo y Hy) (from left to right).

We will prove - (x * (- y)) = x * y.

rewrite the current goal using mul_SNo_minus_distrR x y Hx Hy (from left to right).

We will prove - - (x * y) = x * y.

An exact proof term for the current goal is minus_SNo_invol (x * y) (SNo_mul_SNo x y Hx Hy).

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