Let x0 of type ι be given.
Assume H1: 1 ∈ x0.
Let x1 of type ι be given.
Let x2 of type ι be given.
Apply unknownprop_b040cfab3ba6ec1b3c19f31a88b1921bdc8dd61135c4cd923e1212599f8218e3 with
x0,
x2 leaving 3 subgoals.
The subproof is completed by applying H0.
The subproof is completed by applying H1.
Apply ordinal_Hered with
x1,
(λ x3 . SetAdjoin x3 (Sing x0)) x2 leaving 2 subgoals.
The subproof is completed by applying H2.
The subproof is completed by applying H3.