Used simplifier rules: ls-neg: ⊦ i < 0 → (i * j < i * j0 ↔ j0 < j);%associativity: ⊦ i * j * j0 = (i * j) * j0;%commutativity: ⊦ i * j = j * i;%irref: ⊦ ¬ i < i; from specification int-basic1