m-(N,N'-Dimethylamino) benzoic acid

This article extends snake lemma to two snakes lermma,and entends 3×3 lemma to 3×n lemma 3×3×3 lemma,Moreover,it studies some problems on exact plane,exact cube as well as problems on cubic commtative diagrams.

将蛇引理推广到双蛇引理,将3×3引理推广到3×n引理、3×3×3引理,并研究了与正合平面、正合立体有关的几个问题及立体交换图问题。