The thinking about the product of infinite infinitesimals .
关于无穷多个无穷小的乘积的一些思考。
Calculus has practical applications , such as understanding the true meaning of the infinitesimals .
微积分有著实际的应用，比如理解无穷小的真正含义。
Leibniz discussed with his english colleagues his interest in summing series and the geometry of infinitesimals , and he corresponded with them when he was back in france .
