. intros hneg
  apply h
  apply List.Mem.tail _ hneg
case cons.inr.h
α : Type u_1
inst✝ : DecidableEq α
x : α
a : α × Nat
as : List (α × Nat)
ih : ¬x ∈ map Prod.fst as → map Prod.fst (incrCounts as x) = map Prod.fst as ++ [x]
h : ¬x ∈ map Prod.fst (a :: as)
hneq : ¬a.fst = x
⊢ ¬x ∈ map Prod.fst as
no goals