exact this hmem
case h.h
κ : Type u_1
inst✝ : DecidableEq κ
ν : Type u_2
k : κ
v : ν
xs : List (κ × ν)
hterm : length (matchKey xs k).snd < Nat.succ (length xs)
ih : length (groupByKey (matchKey xs k).snd) = length (unique (map Prod.fst (matchKey xs k).snd))
x : κ
hmem : x ∈ map Prod.fst (matchKey xs x).snd
hneg : x = k
this : ¬x ∈ map Prod.fst (matchKey xs x).snd
⊢ False
no goals