Image:Snake lemma nat.png

A commutative diagram with exact rows, to show the naturality of the snake lemma. Produced with TeX and XY-Pic using the source code below. Both the image and the source code are in the public domain.

% Produce a postscript file from this input with tex and dvips.

% Loading the XY-Pic package:
\input xy
\xyoption{all}

% Using postscript driver for smoother curves
\xyoption{ps}
\xyoption{dvips}

% No need for page numbers
\nopagenumbers

$$
\xymatrix{ %Our diagram is a 4x10 matrix
&&&A_2\ar[rr]\ar[dd]|\hole^(.36){a_2}&&B_2\ar[rr]\ar[dd]|\hole^(.36){b_2}&&C_2\ar[rr]\ar[dd]|\hole^(.36){c_2}&&0\\
&&A_1\ar[rr]\ar[dd]^(.36){a_1}\ar[ur]&&B_1\ar[rr]\ar[dd]^(.36){b_1}\ar[ur]&&C_1\ar[rr]\ar[dd]^(.36){c_1}\ar[ur]&&0\\
&0\ar[rr]|\hole&&A'_2\ar[rr]|\hole&&B'_2\ar[rr]|\hole&&C'_2&&\\
0\ar[rr]&&A'_1\ar[rr]\ar[ur]&&B'_1\ar[rr]\ar[ur]&&C'_1\ar[ur]&&
}
$$

\end

From http://en.wikipedia.org/wiki/Image:Snake_lemma_nat.png

29 January 2004

Axel Boldt

"Both the image and the source code are in the public domain." and "Since I believe that "intellectual property rights" do not exist (as we mere mortals cannot arrogate the right to own parts of Plato's eternal heaven of ideas), every word I write is by default, and always, in the public domain." ([1])