Let x0 of type ι be given.
Let x1 of type ι → ι → ι be given.
Let x2 of type ι be given.
Let x3 of type ι be given.
Assume H2:
∀ x4 . prim1 x4 x0 ⟶ x1 x2 x4 = x4.
Assume H3:
∀ x4 . prim1 x4 x0 ⟶ x1 x4 x3 = x4.
Apply H3 with
x2,
λ x4 x5 . x4 = x3 leaving 2 subgoals.
The subproof is completed by applying H0.
Apply H2 with
x3.
The subproof is completed by applying H1.