public static String[] askHashSet(String msg) {
		LinkedList<String> res = new LinkedList<String>();
		boolean carryOn = true;
		System.out.println(msg + " (empty line to finish) :");
		while (carryOn) {
			String aux = ask();
			if (aux.equals(""))
				carryOn = false;
			else if ( Draft.isHash(aux) )
				res.add( aux );
			else
				System.out.println("!!! Not an implemented hash function !!!");
		}
		return res.toArray(new String[0]);
	}