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


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