split
case cons
α : Type u_1
inst✝ : SizeOf α
f : α → Bool
head✝ : α
tail✝ : List α
tail_ih✝ : sizeOf (filter f tail✝) ≤ sizeOf tail✝
⊢ sizeOf
      (match f head✝ with
      | true => head✝ :: filter f tail✝
      | false => filter f tail✝) ≤
    1 + sizeOf head✝ + sizeOf tail✝
case cons.h_1
α : Type u_1
inst✝ : SizeOf α
f : α → Bool
head✝ : α
tail✝ : List α
tail_ih✝ : sizeOf (filter f tail✝) ≤ sizeOf tail✝
x✝ : Bool
heq✝ : f head✝ = true
⊢ sizeOf (head✝ :: filter f tail✝) ≤ 1 + sizeOf head✝ + sizeOf tail✝

case cons.h_2
α : Type u_1
inst✝ : SizeOf α
f : α → Bool
head✝ : α
tail✝ : List α
tail_ih✝ : sizeOf (filter f tail✝) ≤ sizeOf tail✝
x✝ : Bool
heq✝ : f head✝ = false
⊢ sizeOf (filter f tail✝) ≤ 1 + sizeOf head✝ + sizeOf tail✝