let .cons nodup_head (nodup_tail : l.Nodup) := nodup
case cons
α : Type u
β : Type v
inst✝ : DecidableEq α
p : α → Bool
a : α
l : List α
IH : ∀ {l' : List α}, l ⊆ l' → Nodup l → countP p l ≤ countP p l'
l' : List α
hsub : a :: l ⊆ l'
nodup : Nodup (a :: l)
⊢ countP p (a :: l) ≤ countP p l'
case cons
α : Type u
β : Type v
inst✝ : DecidableEq α
p : α → Bool
a : α
l : List α
IH : ∀ {l' : List α}, l ⊆ l' → Nodup l → countP p l ≤ countP p l'
l' : List α
hsub : a :: l ⊆ l'
nodup : Nodup (a :: l)
nodup_head : ∀ (a' : α), a' ∈ l → a ≠ a'
nodup_tail : Nodup l
⊢ countP p (a :: l) ≤ countP p l'