# x0 = # x1 + # x2, x1 + x2 ⊑ x0 ⊦ x0 = x1 + x2
Used simplifier rules: a: ⊦ (x + y) + z = x + y + z; from specification list% ⊦ x ⊑ x; (s)% ⊦ x + y ⊑ x + z ↔ y ⊑ z; (s)