Let x0 of type ι be given.
Let x1 of type ι be given.
Assume H1: x1 ∈ x0.
Let x2 of type ι be given.
Apply ordsuccE with
x1,
x2,
x2 ∈ x0 leaving 3 subgoals.
The subproof is completed by applying H2.
Assume H3: x2 ∈ x1.
Apply H0 with
x1,
x2 leaving 2 subgoals.
The subproof is completed by applying H1.
The subproof is completed by applying H3.
Assume H3: x2 = x1.
Apply H3 with
λ x3 x4 . x4 ∈ x0.
The subproof is completed by applying H1.