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,
x1.
The subproof is completed by applying unknownprop_4d1134395428f655c70060d89bfb8558ccadeb21955f223d5ca8f7e2fc67148c with x0, x1, x2, x3.