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:
<coq-core.plugins.ssreflect::ssrtcldo@0> arg