Goal:
  
  A : Type
  H : ReflectEq A
  a1 : A
  l1 : list A
  a2 : A
  l2 : list A
  Heq : (a1 == a2) = false
  l0 : list A
  l3 : list A
  ============================
   (∀ l : list A,
      {| pr1 := a1 :: l1; pr2 := a2 :: l2 |} = {| pr1 := l0; pr2 := l3 |}
      → ([], a1 :: l1, a2 :: l2) = split_prefix l0 l3
        → let H := CoreTactics.block in
          is_prefix l l0
          → is_prefix l l3 → is_prefix l (fst (fst (split_prefix l0 l3))))


DEBUG:Going to execute:
let H := fresh x in
           intro
           H
Level 3: Backtrace:

The first hypothesis in the goal is not an equality.
Level 3: Backtrace:

The first hypothesis in the goal is not an equality.
Level 3: Backtrace:

The first hypothesis in the goal is not an equality.
Level 3: Backtrace:

The first hypothesis in the goal is not an equality.