quiver pictures in wordpress

Having latexrender available, one can edit the class.latexrender.php file to include additional LaTeX-packages. For example adding the lines

 
string .= '\usepackage{xy}\n';  
string .= '\xyoption{all}\n';  
string .= '\newcommand{\vtx}[1]{*+[o][F-]{\scriptscriptstyle #1}}\n';

makes it possible to include quiver-pictures in this weblog. Observe the double blackslash before newcommand, a single backslash would produce a new-line and fail to define something.