clear heq
case intro.hmotive
α : Type u_1
v x : α
L : List α
hL : ↑L = {x}.val
heq :
  elim {x}
      (fun L _hL =>
        match L, _hL with
        | [], _hL => ⋯.elim
        | x_1 :: tail, _hL => x_1)
      ⋯ =
    match L, hL with
    | [], _hL => ⋯.elim
    | x_1 :: tail, _hL => x_1
⊢ (match L, hL with
      | [], _hL => ⋯.elim
      | x_1 :: tail, _hL => x_1) =
      v ↔
    x = v
case intro.hmotive
α : Type u_1
v x : α
L : List α
hL : ↑L = {x}.val
⊢ (match L, hL with
      | [], _hL => ⋯.elim
      | x_1 :: tail, _hL => x_1) =
      v ↔
    x = v