Let m and n be given.
Apply H1 to the current goal.
Assume H.
Apply H to the current goal.
Assume H.
Apply H to the current goal.
Let k be given.
Assume H.
Apply H to the current goal.
Apply and3I to the current goal.
An exact proof term for the current goal is Hm.
An exact proof term for the current goal is Hn.
We use
- k to
witness the existential quantifier.
Apply andI to the current goal.
An exact proof term for the current goal is Hk.
We will
prove m * (- k) = - n.
We will
prove - m * k = - n.
Use f_equal.
An exact proof term for the current goal is H2.
∎