Goal:
  
  A : Type
  H : ReflectEq A
  l1 : list A
  l2 : list A
  _a_ : list A
  _b_ : list A
  _b1_ : list A
  ============================
   (l1 = rev _b_ ++ rev _a_
    → l2 = rev _b1_ ++ rev _a_
      → l1 = rev _b_ ++ rev _a_ ∧ l2 = rev _b1_ ++ rev _a_)


DEBUG:Going to execute:
hnf