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.
Let x5 of type ι be given.
Apply binunionI1 with
SetAdjoin (SetAdjoin (SetAdjoin (UPair x0 x1) x2) x3) x4,
Sing x5,
x3.
The subproof is completed by applying unknownprop_bce292dbf3466a71711d948e5a5b744a6432721deb4655ed1a8e9dc5653d01b1 with x0, x1, x2, x3, x4.