rw [←Nat.add_assoc]
case cons.isFalse
κ : Type u_1
ν : Type u_2
inst : DecidableEq κ
k : κ
x : κ × ν
xs : List (κ × ν)
ih : length (matchKey xs k).fst + length (matchKey xs k).snd = length xs
hfalse : ¬x.fst = k
⊢ length (matchKey xs k).fst + (length (matchKey xs k).snd + 1) = length xs + 1
case cons.isFalse
κ : Type u_1
ν : Type u_2
inst : DecidableEq κ
k : κ
x : κ × ν
xs : List (κ × ν)
ih : length (matchKey xs k).fst + length (matchKey xs k).snd = length xs
hfalse : ¬x.fst = k
⊢ length (matchKey xs k).fst + length (matchKey xs k).snd + 1 = length xs + 1