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,
x1 leaving 2 subgoals.
The subproof is completed by applying H0.
The subproof is completed by applying unknownprop_70f06371245ce38fbbca963cb4d7e422ccf350d2e27735c617635b09cbcba701 with x0, x1.