Goal:
  
  A : Type
  H : ReflectEq A
  a : A
  l : list A
  l1 : list A
  l2 : list A
  l0 : list A
  ============================
   ({| pr1 := a :: l; pr2 := [] |} = {| pr1 := l1; pr2 := l2 |}
    → ([], a :: l, []) = split_prefix l1 l2
      → let H := CoreTactics.block in
        is_prefix l0 l1
        → is_prefix l0 l2 → is_prefix l0 (fst (fst (split_prefix l1 l2))))


DEBUG:Going to execute:
simplify * || simplify ?