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,
x3.
The subproof is completed by applying unknownprop_7b54ca399582282a7040a71f9c2f008cb6ef4ffaa1dd688f4883cd33f8f6980b with x0, x1, x2, x3.