Let x0 of type ι be given.
Let x1 of type ι be given.
Let x2 of type ι be given.
Let x3 of type ι be given.
Apply H0 with
x3,
prim1 x3 x2 ⟶ prim1 x3 x1 leaving 2 subgoals.
The subproof is completed by applying H1.
The subproof is completed by applying H3.