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.
Let x4 of type ι be given.
Apply binunionI1 with
SetAdjoin (SetAdjoin (UPair x0 x1) x2) x3,
Sing x4,
x0.
The subproof is completed by applying unknownprop_a83b0f00b7010506012eac50a37acf9397f188fab2e100b8a543b795c63cc457 with x0, x1, x2, x3.