Let x0 of type ι be given.
Let x1 of type ι be given.
Apply In_irref with
ordsucc (add_SNo x0 x1).
Apply add_SNo_ordinal_SL with
x0,
x1,
λ x2 x3 . ordsucc (add_SNo x0 x1) ∈ x2 leaving 3 subgoals.
The subproof is completed by applying H0.
The subproof is completed by applying H1.
The subproof is completed by applying H9.