urec.lean:3:0: error: invalid user defined recursor, result type must be of the form (C t), where C is a bound variable, and t is a (possibly empty) sequence of bound variables
urec.lean:5:0: error: invalid user defined recursor, 'nat.rec' is a builtin recursor
urec.lean:19:0: error: invalid user defined recursor, type of the major premise 'a' must be for the form (I ...), where I is a constant
myrec.{l_1 l_2} :
  Π (A : Type.{l_1}) (M : list.{l_1} A → Type.{l_2}) (l : list.{l_1} A),
    M (@nil.{l_1} A) → (Π (a : A), M [a]) → (Π (a₁ a₂ : A), M [a₁, a₂]) → M l
recursor information
  num. parameters:          1
  num. indices:             0
  universe param pos.:      0 [motive univ]
  motive pos.:              2
  major premise pos.:       3
  dep. elimination:         1
  parameters pos. at major: 1
recursor information
  num. parameters:          0
  num. indices:             0
  universe param pos.:     
  motive pos.:              1
  major premise pos.:       2
  dep. elimination:         1
vector.induction_on.{l_1} :
  ∀ {A : Type.{l_1}} {C : Π (a : ℕ), vector.{l_1} A a → Prop} {a : ℕ} (n : vector.{l_1} A a),
    C 0 (@vector.nil.{l_1} A) →
    (∀ {n : ℕ} (a : A) (a_1 : vector.{l_1} A n), C n a_1 → C (nat.succ n) (@vector.cons.{l_1} A n a a_1)) →
    C a n
recursor information
  num. parameters:          1
  num. indices:             1
  universe param pos.:      0
  motive pos.:              2
  major premise pos.:       4
  dep. elimination:         1
  parameters pos. at major: 1
  indices pos. at major:    2
Exists.rec.{l_1} :
  ∀ {A : Type.{l_1}} {P : A → Prop} {C : Prop},
    (∀ (a : A), P a → C) → @Exists.{l_1} A P → C
recursor information
  num. parameters:          2
  num. indices:             0
  universe param pos.:      0
  motive pos.:              3
  major premise pos.:       5
  dep. elimination:         0
  parameters pos. at major: 1 2