public boolean prefixFreeAux(Node node,boolean checked){
		boolean check=false;
		boolean end=false;
		
		if (node==null) return true;
		
		if (!node.name.isEmpty()) { //Eliminate root node.
			check=node.isUsed();
		
			if (check && checked) {
				return false; //Non prefix Free.
			}
			else {
				checked=check|checked;  // Super or working node selected
			}
		}
		
		end=prefixFreeAux(node.leftChild,checked);
		if (end) end=prefixFreeAux(node.rightChild,checked);
		
		return end;
}