Let x0 of type ι be given.
Let x1 of type ι be given.
Let x2 of type ι be given.
Apply and3I with
SNo x1,
SNoLev x1 ∈ SNoLev x0,
SNoLt x0 x1 leaving 3 subgoals.
The subproof is completed by applying H1.
The subproof is completed by applying H3.
The subproof is completed by applying H0.