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.
Let x6 of type ι be given.
Apply binunionI1 with
SetAdjoin (SetAdjoin (SetAdjoin (SetAdjoin (UPair x0 x1) x2) x3) x4) x5,
Sing x6,
x0.
The subproof is completed by applying unknownprop_026a02ec2a61d9b71e75f37f5c8c8ef312184a8db8726e8eb929b169123db6f2 with x0, x1, x2, x3, x4, x5.