The following program was written by Davide Brini
and is published on his website.
It serves as his signature in the Usenet group comp.lang.awk.
He supplies the following copyright terms:
Copyright © 2008 Davide Brini
Copying and distribution of the code published in this page, with or without modification, are permitted in any medium without royalty provided the copyright notice and this notice are preserved.
Here is the program:
awk 'BEGIN{O="~"~"~";o="=="=="==";o+=+o;x=O""O;while(X++<=x+o+o)c=c"%c";
printf c,(x-O)*(x-O),x*(x-o)-o,x*(x-O)+x-O-o,+x*(x-O)-x+o,X*(o*o+O)+x-O,
X*(X-x)-o*o,(x+X)*o*o+o,x*(X-x)-O-O,x-O+(O+o+X+x)*(o+O),X*X-X*(x-O)-x+O,
O+X*(o*(o+O)+O),+x+O+X*o,x*(x-o),(o+X+x)*o*o-(x-O-O),O+(X-x)*(X+O),x-O}'
We leave it to you to determine what the program does. (If you are truly desperate to understand it, see Chris Johansen’s explanation, which is embedded in the Texinfo source file for this Web page.)