public Parser subtractStatement() {
        if (subtractStatementParser == null) {
           FutureParser future = scoped("subtractStatement");
           subtractStatementParser = future;
           future.setParser(
               sequence(
                   token("SUBTRACT"),
                   choice(
                       subtraction_format1(),
                       subtraction_format2(),
                       subtraction_format3()
                   ),
                   optional(
                       sequence(
                           optional(
                               token("ON")
                           ),
                           token("SIZE"),
                           token("ERROR"),
                           nestedStatements()
                       )
                   ),
                   optional(
                       sequence(
                           token("NOT"),
                           optional(
                               token("ON")
                           ),
                           token("SIZE"),
                           token("ERROR"),
                           nestedStatements()
                       )
                   ),
                   optional(
                       token("END-SUBTRACT")
                   )
               )
           );
        }

        return subtractStatementParser;
    }