<?xml version='1.0' encoding='us-ascii'?>
<!--  DTD for a simple "math".  -->

<!ELEMENT apply (
   (minus, (cn | ci | apply))
 | ( (minus | divide | power), (cn | ci | apply), (cn | ci | apply))
 | ( (plus | times), (cn | ci | apply)*)
                )>

<!ELEMENT minus  (empty)>
<!ELEMENT divide (empty)>
<!ELEMENT power  (empty)>
<!ELEMENT plus   (empty)>
<!ELEMENT times  (empty)>
<!ELEMENT cn   (#PCDATA)>
<!ELEMENT ci   (#PCDATA)>