LaTeX / pdfTeX / XeLaTeX / XeTeX hanging

The error is that when running LaTeX or XeLaTeX, there is an infinite freeze or hang with no error messages, and CTRL-C is needed to stop the process.


I managed to cause this problem by having the following definition in my header:


Apparently using \renewcommand to create a recursive definition will cause a hang. Instead, it should have read (in my case):


I suspect that any recursive definition like this will probably cause a hang.