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
  ============================
   ({| pr1 := a1 :: l1; pr2 := a2 :: l2 |} = {| pr1 := l0; pr2 := l3 |}
    → ([], a1 :: l1, a2 :: l2) = split_prefix l0 l3
      → let H := CoreTactics.block in
        let
        '(prefix, l1', l2') := split_prefix l0 l3 in
         l0 = prefix ++ l1' ∧ l3 = prefix ++ l2')


DEBUG:Going to execute:
simplify *