Apply In_ind with
λ x0 . ∀ x1 . x0 ∈ x1 ⟶ x1 ∈ x0 ⟶ False.
Let x0 of type ι be given.
Assume H0:
∀ x1 . x1 ∈ x0 ⟶ ∀ x2 . x1 ∈ x2 ⟶ x2 ∈ x1 ⟶ False.
Let x1 of type ι be given.
Assume H1: x0 ∈ x1.
Assume H2: x1 ∈ x0.
Apply H0 with
x1,
x0 leaving 3 subgoals.
The subproof is completed by applying H2.
The subproof is completed by applying H2.
The subproof is completed by applying H1.