Goal:
    A : Type  H : ReflectEq A  a1 : A  l1 : list A  a2 : A  l2 : list A
  ============================
   ((a1 == a2) = false
    → ∀ (H := CoreTactics.block) (l3 l4 : list A),
        {| pr1 := a1 :: l1; pr2 := a2 :: l2 |} = {| pr1 := l3; pr2 := l4 |}
        → ([], a1 :: l1, a2 :: l2) = split_prefix l3 l4
          → let H0 := CoreTactics.block in
            let
            '(prefix, l1', l2') := split_prefix l3 l4 in
             l3 = prefix ++ l1' ∧ l4 = prefix ++ l2')


DEBUG:Going to execute:
simplify * || simplify ?; cbv beta