∀ i, j. i + j + i1 = (i + j) + i1 ⊦ i + j + i1 = (i + j) + i1
Used simplifier rules: add-succ: ⊦ i + j +1 = (i + j)+1;%succ-in: ⊦ i +1 = j +1 ↔ i = j; from specification int-basic1