It doesn't. The rule for TeX is that single-character tokens don't need braces. I assume this is just an artefact of their particular muscle memory. You can te

It doesn't. The rule for TeX is that single-character tokens don't need braces. I assume this is just an artefact of their particular muscle memory. You can test it here, if you like: https://www.mathjax.org/#demo https://www.mathjax.org/#demo