`\let` handled incorrectly

[dimitriye98]

Issue Summary

MathJax aliases let to \newcommand, but this breaks code which uses \let and \renewcommand together.

Minimal example:

\let\test\approx
\renewcommand{\approx}{\test\test}
$\approx$

In LaTeX this will produce ≈≈. In MathJax however, it causes a stack overflow due to infinite recursion.

Related to James-Yu/LaTeX-Workshop#2035

[dpvc]

MathJax aliases let to \newcommand

This statement is incorrect. MathJax processes \let differently than \newcommand, and does handle your situation correctly in both v3 and v2.

Of course, MathJax only processes macros in math mode, so would not process that \let and \renewcommand as they are in your example (outside of math mode), so I suspect some other system is being used to turn the original LaTeX into something that is eventually sent to MathJax, and it is that system that is treating \let as \newcommand.

When you obtain your final HTML page, you might check the source (via view source) to see if it uses \let or \newcommand.

In any case, you can test that MathJax handles your situation using one of the demo pages that allow arbitrary input, say the tex2chtml demo by entering

\let\test\approx
\renewcommand{\approx}{\test\test}
\approx

(with no dollar signs, as what you enter is already in math mode).

So I'm not sure where the problem you are having originates, but it is not from MathJax, and is most likely from LaTeX-Workshop's processing of the definitions prior to sending them to MathJax.

[dimitriye98]

My bad, before making this issue I tested it in https://www.mathjax.org/#demo to confirm the problem and the demo there threw a "MathJax maximum macro substitution count exceeded; is there a recursive macro call?", however, testing it again, it seems like it's merely a problem with the page, since refreshing the page makes it start working, but clicking "Render HTML" again will break with the aforementioned error.

[dpvc]

The MathJax demo is just a very simple thing, and the definitions from previous runs will still be in effect. So when you render it a second time, \approx has been redefined as \test\test and you are letting \test equal to that, so when \approx is replaced by \test\test, that becomes \test\test\test\test and then \test\test\test\test\test\test\test\test and so on, infinitely. You would have to reload the page to clear the definitions.