capacity exceeded…

A silly LaTeX error took me a few minutes too many to solve: I defined

\renewcommand\theta{\boldsymbol{\theta}}

which got me the error message

TeX capacity exceeded , 
sorry [ grouping levels =255].

that I understood as a recursive definition. So I instead pre-defined the new θ as

\newcommand\btheta{\boldsymbol{\theta}}
\renewcommand\theta\btheta

which did not work either… After google-ing the issue, I found this on-line LaTeX Wikibook that provided me with the solution:

\let\btheta{\boldsymbol{\theta}}
\renewcommand\theta\btheta

which worked. Of course, a global change of \theta into \btheta would have been much much faster to execute….