(Program
  (ExpressionStatements
    (Object
      (Method
      { (Identifier)
      ->(Identifier) }
        (Params
          (Other "required_parameter"
            (Identifier))
          (Other "required_parameter"
            (Identifier)))
        (Return
          (MathOperator
            (Identifier)
          { (Other "-")
          ->(Other "+") }
            (Identifier)))))))