Let x0 of type ο be given.
Apply unknownprop_1e0cb2b8ae8b2a70437458035764f08e7eaba30fc84a0048f28b1466366514c4 with
x0.
Apply unknownprop_e284d5f5a7c3a1c03631041619c4ddee06de72330506f5f6d9d6b18df929e48c with
not x0.
The subproof is completed by applying H0.