(Program
{-(Return
    (
      (Plus
        (Identifier)
        (
          (Identifier)))
      (Identifier)))-}
  (Return
    (Empty))
  (Return
  { (Not
      (Identifier))
  ->(
      (Plus
        (Identifier)
        (
          (Identifier)))
      (Identifier)) })
{+(Return
    (Not
      (Identifier)))+})