说明：  一种 AUTO_CAD 二次开发的LISP程序，题目的难点在与求直线与圆的切点。对于编写LISP程序的初学者有些许的帮助
(AUTO_CAD a secondary development of LISP procedures, the subject of difficult and demand in a straight line with a circle cut-off point. LISP procedures for the preparation of some promises to help beginners)