request for help!

hi all,
   i am a beginner on javacc. this question has confused me so long
time,i can't check the mistakes,so here request for help.
   Here is the source code,listed as follows.it is about boolean
expression evaluation program.for example: if (89>9 and 'a'>'b') is
false ,then print false.
my question is that  the second expression ('a'>'b')after 'and',can't
be parsed every time.i can't find the reason.please help me .
  Thanks for any reply!

PARSER_BEGIN(Exper)
public class Exper{

}
PARSER_END(Exper)
/*number */
TOKEN:{
<NUMBER: (["0"-"9"])+ >
}

/*operator*/
TOKEN:{
 <LPAREN: "(">
|<RPAREN: ")">
|<LT: "<">
|<GT: ">">
|<LE: "<=">
|<GE: ">=">
|<EQ: "==">
|<NE: "!=">
|<AND: "and">
|<OR: "or">
|<NOT: "not">
}


/*white space*/
SKIP:
{" "|"\n"|"\r"|"\t"
}

/*quoted String */
TOKEN:{<STRING:
 "\'"  (~["\n","\r","\'"])* "\'">
}

Boolean exp():
{Boolean l,r;}
{ l=lex(){return l;} (<AND> r=lex()
                         {
                           if(l.booleanValue()&& r.booleanValue())
                                  return Boolean.TRUE;
                           else
                                return Boolean.FALSE;}
|<OR> r=lex()  {if (l.booleanValue()||r.booleanValue())
                   return Boolean.TRUE;
               else
                   return Boolean.FALSE;
     })*
}

Boolean lex():
{ Boolean t;}
{ <NOT> t=rex(){ if(t.booleanValue())
     return Boolean.FALSE;
   else
     return Boolean.TRUE;}
|t=rex(){return t;}
}
Boolean rex():
{ Boolean t;
  Object l,r; }
{ l=atom()
        (<GT> r=atom(){return Util.gt(l,r);}|<LT>r=atom(){return
Util.lt(l,r);}|
     <GE>r=atom(){return Util.ge(l,r);}|<LE>r=atom(){return
Util.le(l,r);}|<EQ>r=atom(){return Util.eq(l,r);}
   | <NE>r=atom(){return Util.ne(l,r);})*

  }

Object  atom():
{
  Token t,str;
  Boolean s;}
{ t=<NUMBER>{return new Double(t.image);}|str=<STRING>{return
(str.image.substring(1,str.image.length()-1));}|
 <LPAREN>s=exp(){ return s; }<RPAREN>
}