I was cleaning up my LaTeX header and re-coded some macros to suit my needs better. I have always had a macro called `\of` which takes one parameter. It used to be the very simple macro ```Latex \newcommand{\of}[1]{\left(#1\right)} ``` However, I sometimes want to specify the size of the brackets explicitly, so I wanted to add an optional argument to this macro such that `\of[big]{\sum}` will expand to `\bigl(\sum\bigr)`. Sometimes I even want it not to do any resizing of the brackets at all. The correct way to do this is is `\csname` and `\endcsname` which allows you to delay expansion of a macro. Inside a macro definition, the command ```Latex \newcommand{\ar}[1]{\csname#1arrow\endcsname} ``` will be such that `\ar{right}` is first made into `\rightarrow` and <i>then</i> expanded. We will use that to make `\bigl` and `\bigr` out of the argument `big`, for instance. <a href="https://blag.nullteilerfrei.de/2014/01/16/a-dynamic-bracketing-macro-in-latex/#more-2369" class="more-link">Do you want to know more?</a>