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,
x2.
The subproof is completed by applying unknownprop_e4760fc821f351cd9b641f80133df8c2736e77957d5436be4e26fe6dae8c4afe with x0, x1, x2, x3.