∃ d. a × d ∈ ax ∨ a × d ∈ ay ⊦ ∃ d. a × d ∈ ax, ∃ d. a × d ∈ ay
(∃ d. a × d ∈ ax) ∨ (∃ d. a × d ∈ ay) ⊦ ∃ d. a × d ∈ ax ∨ a × d ∈ ay