Let x0 of type ι be given.
Let x1 of type ι be given.
Let x2 of type ι be given.
Apply UnionI with
prim2 x0 x1,
x2,
x0 leaving 2 subgoals.
The subproof is completed by applying H0.
The subproof is completed by applying unknownprop_893870ab8a49d622c10a8fe954eea30d7bd2b94aa27e9c6b21eab85a9f81d115 with x0, x1.