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.ltac::trivial@0> $1 $2