code: private PExp getExistsPredicate(AMapCompMapExp exp, ILexNameToken finmap,
  			ILexNameToken findex)
  	{
  		AApplyExp apply = getApplyExp(getVarExp(finmap), getVarExp(findex));
  
  		AMapEnumMapExp setEnum = new AMapEnumMapExp();
  		List<AMapletExp> members = new Vector<AMapletExp>();
  		members.add(exp.getFirst().clone());
  		setEnum.setMembers(members);
  
  		return getEqualsExp(apply, setEnum);
  	}
docs: m(idx) = { a |-> b }