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,
x0.
The subproof is completed by applying unknownprop_56452fe06aca82d310983388ec25d56a97f31b883325980403ff02c27aa4e5f6 with x0, x1, x2, x3, x4.