⊦ a ∈ rmdup((x + y) + z) ↔ a ∈ rmdup(x + z), a ∈ y
User applied rule case distinction
And closed the goal!
Rule argument
pos: right 1
Additional information
Used simplifier rules:
⊦ a ∈ rmdup(x + y) ↔ a ∈ x ∨ a ∈ y; (ws)% ⊦ a ∈ x + y ↔ a ∈ x ∨ a ∈ y; (s)%a: ⊦ (x + y) + z = x + y + z; from specification list