(Program
  (If
    (Send
    { (Identifier)
    ->(Identifier) })
    (
    {+(Send
      {+(Identifier)+})+})
  { (Empty)
  ->(If
    {+(Send
      {+(Identifier)+})+}
    {+(
      {+(Send
        {+(Identifier)+})+})+}
    {+(Send
      {+(Identifier)+})+}) })
{-(If
  {-(Send
    {-(Identifier)-})-}
  {-([])-}
  {-(Empty)-})-})