http://www.cplusplus.com/doc/tutorial/namespaces/

http://publib.boulder.ibm.com/infocenter/compbgpl/v9v111/index.jsp?topic=/com.ibm.xlcpp9.bg.doc/language_ref/cplr384.htm

http://www.cprogramming.com/tutorial/operator_overloading.html

http://www.ozzu.com/cpp-tutorials/tutorial-defining-and-overloading-operators-t85776.html