Let x0 of type ι be given.
Let x1 of type ι be given.
Apply unknownprop_c3fe42b21df0810041479a97b374de73f7754e07c8af1c88386a1e7dc0aad10f with
x0,
binunion x0 x1.
The subproof is completed by applying unknownprop_1598d20a62a395ced156dfcc7d767ab023594ea6ef7c5e3b53cecdbebaf0ec29 with x0, x1.