⊦ (∃ d. a × d ∈ ax ∨ a × d ∈ ay) ↔ a ∈ ax ∨ a ∈ ay
Used simplifier rules: a: ⊦ (ax + ax0) + ax1 = ax + ax0 + ax1; from specification list[assoclist]% ⊦ p ∈ ax + ax0 ↔ p ∈ ax ∨ p ∈ ax0; (s)