Two books on calculus by Leibniz were apparently published posthumously by his secretary [Rafael Levi](http://en.wikipedia.org/wiki/Raphael_Levi_Hannover), see http://opac.tib.uni-hannover.de/DB=1/LNG=EN/CHARSET=iso-8859-1/CMD?ACT=SRCHA&IKT=1016&SRT=YOP&TRM=Raphael+Levi&Submit=go Does anyone know anything about those books? What's in them?