Because apparently, some people our age still do not know about the Pilot Frixion Pen1, let me just very briefly inform you about this ingenious item. It is a regular ball pen, but the ink it uses turns invisible under a certain amount of heat. Hence, the Frixion has a little rubber nob at the end, which effectively works as an eraser, because rubbing it against a sheet of paper produces enough heat to turn the ink invisible! Good news: Leaving your lecture notes on the heating does not erase them. Seriously though, this pen is just awesome.