simp_rw [posDiffs, mem_image, mem_filter, mem_product, Prod.exists, and_assoc, exists_and_left]
α : Type u_1
inst✝² : GeneralizedBooleanAlgebra α
inst✝¹ : DecidableRel fun x x_1 => x ≤ x_1
inst✝ : DecidableEq α
s t : Finset α
a : α
⊢ a ∈ s \₊ t ↔ ∃ b ∈ s, ∃ c ∈ t, c ≤ b ∧ b \ c = a
no goals