ambiguous formula parser

package szabivan.cup;

import java_cup.runtime.*;
import formula.data.*;

class FormulaParser;

terminal VEE, WEDGE, IMPLIES, IFF, LPAREN, RPAREN, UP, DOWN, NEGATION;
terminal String VARIABLE;

non terminal Formula formula;

formula ::= 	VARIABLE |
		LPAREN formula RPAREN |
		formula VEE formula |
		formula WEDGE formula |
		formula IMPLIES formula |
		formula IFF formula |
		NEGATION formula |
		UP |
		DOWN
		;