| ⊦ [] ++ a = a ' |
Used simplifier rules: adjoin-in: ⊦ a ∈ x → x ++ a = x;%adjoin-notin: ⊦ ¬ a ∈ x → x ++ a = a + x;%c: ⊦ a + x = a ' + x; from specification list%app: ⊦ x + [] = x; from specification list%a: ⊦ (x + y) + z = x + y + z; from specification list%c-04: ⊦ a ' = b ' ↔ a = b; from specification list%e: ⊦ a ' ≠ []; from specification list%in-empty: ⊦ ¬ a ∈ []; from specification list Used formulas: a ∈ []