private Expr expr() {
		Expr res, nextTerm;	res = term();
		while (theTokenizer.ttype == '+' || theTokenizer.ttype == '-') {
			char op = (char) theTokenizer.ttype;
			theTokenizer.next();
			nextTerm = term();
			if (op == '+') {
				res = new Add(res,nextTerm);
			} else {
				res = new Sub(res,nextTerm);
			}
		}
		return res;
	}