α : Type u_1
inst✝ : CoheytingAlgebra α
a b : α
⊢ a ⊓ ￢(a ⊔ b) ⊔ b ⊓ ￢(a ⊔ b) ≤ ∂ a ⊔ ∂ b
α : Type u_1
inst✝ : CoheytingAlgebra α
a b : α
⊢ ∂ (a ⊔ b) ≤ ∂ a ⊔ ∂ b
rw [boundary, inf_sup_right]
no goals
α : Type u_1
inst✝ : CoheytingAlgebra α
a b : α
⊢ a ⊓ ￢(a ⊔ b) ⊔ b ⊓ ￢(a ⊔ b) ≤ ∂ a ⊔ ∂ b
exact
  sup_le_sup (inf_le_inf_left _ <| hnot_anti le_sup_left)
    (inf_le_inf_left _ <| hnot_anti le_sup_right)