apply List.countP_disjoint
α : Type u
β : Type v
inst✝³ : BishopFin α
inst✝² : BishopFin β
p q : α → Prop
inst✝¹ : DecidablePred p
inst✝ : DecidablePred q
h : ∀ (a : α), ¬(p a ∧ q a)
⊢ List.countP (fun a => decide (p a) || decide (q a)) (elems α) =
    List.countP (fun a => decide (p a)) (elems α) + List.countP (fun a => decide (q a)) (elems α)
case h
α : Type u
β : Type v
inst✝³ : BishopFin α
inst✝² : BishopFin β
p q : α → Prop
inst✝¹ : DecidablePred p
inst✝ : DecidablePred q
h : ∀ (a : α), ¬(p a ∧ q a)
⊢ ∀ (a : α), (decide (p a) && decide (q a)) = false