Goal:
  
  A : Type
  H : ReflectEq A
  l : list A
  _x_ : list A
  a : A
  l0 : list A
  p : [] = (a :: l0) ++ _x_
  ============================
   (a :: l0 = [])


DEBUG:Going to execute:
apply : eq_sym ; trivial
Level 0: Backtrace:

Proof is not complete.
Level 0: Backtrace:

Proof is not complete.