⊦ dups(a ' + b ' + x) ↔ b ∈ x, a = b, dups(x), a ∈ x
Heuristic simplifier applied rule simplifier
And closed the goal!
Rule argument
Additional information
Used simplifier rules:
rec: ⊦ dups(a ' + x) ↔ a ∈ x ∨ dups(x);%a: ⊦ (x + y) + z = x + y + z; from specification list% ⊦ a ≠ b → (a ∈ b ' + x ↔ a ∈ x); (s)