| sort(x1 + a ' + x0) = sort(x1 + x0) + a ', (max(x1 + x0) < a ⊃ a;max(x1 + x0)) < max(sort(x1 + x0) + a '), max(x1 + x0) < max(sort(x1 + x0) + a '), a < max(sort(x1 + x0) + a '), max(x1 + x0) < a, ordered≤(sort(x1 + x0) + a ') ⊦ x1 + x0 = [], ins≤(a, sort(x1 + x0) + a ') = (sort(x1 + x0) + a ') + a ', a < max(x1 + x0), a < (max(x1 + x0) < a ⊃ a;max(x1 + x0)) |
sort(x1 + a ' + x0) = sort(x1 + x0) + a ', max(x1 + x0) < a, max(x1 + x0) < max(sort(x1 + x0) + a '), a < max(sort(x1 + x0) + a '), ordered≤(sort(x1 + x0) + a ') ⊦ x1 + x0 = [], ins≤(a, sort(x1 + x0) + a ') = (sort(x1 + x0) + a ') + a '
Used simplifier rules: ⊦ a < b → (b < a ↔ false); (ss)% ⊦ ¬ a < a; (s)