| a ∈ x, y ⊆m x -1l a ⊦ #oc(a, x) ≤ #oc(a, y) + 1 ∧ x -1l a ⊆m y ↔ x -1l a ⊆m y |
#oc(a, y) + 1 < #oc(a, x), a ∈ x, x -1l a ⊆m y, y ⊆m x -1l a ⊦
Used simplifier rules: in-05: ⊦ a ∈ x → #oc(a, x) ≠ 0;%f: ⊦ m < n → n ≠ 0; (forward) from specification nat-basic% ⊦ m ≤ n ↔ ¬ n < m; (ss)