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Proofgold Proof

pf
Let x0 of type ι be given.
Let x1 of type ι be given.
Let x2 of type ι be given.
Assume H0: x2x1.
Let x3 of type ι be given.
Assume H1: x3setminus x0 x1.
Apply setminusE with x0, x1, x3, x3setminus x0 x2 leaving 2 subgoals.
The subproof is completed by applying H1.
Assume H2: x3x0.
Assume H3: nIn x3 x1.
Apply setminusI with x0, x2, x3 leaving 2 subgoals.
The subproof is completed by applying H2.
Apply Subq_contra with x2, x1, x3 leaving 2 subgoals.
The subproof is completed by applying H0.
The subproof is completed by applying H3.