<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE structure SYSTEM "grammar.dtd" >
<structure>
	<type>grammar</type>
	<!--The list of productions.-->
	<production>
		<left>S</left>
		<right>aSb</right>
	</production>
	<production>
		<left>S</left>
		<right></right>
	</production>
</structure>