Used simplifier rules: intempty: ⊦ a ∈ x ∧ a ∈ y → list2set(x) ∩ list2set(y) ≠ ∅;% ⊦ s ∩ s0 = s0 ∩ s;% ⊦ (s ∩ s0) ∩ s1 = s ∩ s0 ∩ s1;