(some _private.structuralEqns.0.foo._unfold)
foo._unfold : ∀ (xs ys zs : List Nat),
  foo xs ys zs =
    match (xs, ys) with
    | (xs', ys') =>
      match zs with
      | z :: zs => foo xs ys zs
      | x =>
        match ys' with
        | [] => [1]
        | x => [2]
def bar : List Nat → List Nat → List Nat :=
fun xs ys =>
  match xs ++ [], ys ++ [] with
  | xs', ys' => xs' ++ ys'