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 M l, M (@nil.{l_1} A) → (Π a, M [a]) → (Π a₁ a₂, M [a₁, a₂]) → M l
recursor information
  num. parameters:          1
  num. indices:             0
  num. minors:              3
  recursive:                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
  num. minors:              2
  recursive:                1
  universe param pos.:     
  motive pos.:              1
  major premise pos.:       2
  dep. elimination:         1
vector.induction_on.{l_1} :
  ∀ {A} {C} {a} n,
    C 0 (@vector.nil.{l_1} A) → (∀ {n} a a_1, 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
  num. minors:              2
  recursive:                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} {P} {C}, (∀ a, P a → C) → @Exists.{l_1} A P → C
recursor information
  num. parameters:          2
  num. indices:             0
  num. minors:              1
  recursive:                0
  universe param pos.:      0
  motive pos.:              3
  major premise pos.:       5
  dep. elimination:         0
  parameters pos. at major: 1 2