. exact List.Mem.head _
case cons.cons.inl.hc
α : Type u_1
inst✝ : DecidableEq α
x : α
xs : List α
ih :
  ∀ (acc : List (α × Nat)),
    length (foldl (fun acc v => incrCounts acc v) acc xs) = length (uniqueAux xs (map Prod.fst acc))
a : α × Nat
as : List (α × Nat)
htrue : a.fst = x
⊢ x ∈ x :: map Prod.fst as
no goals