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• CommentRowNumber1.
• CommentAuthorAndrew Stacey
• CommentTimeOct 5th 2010

Not all of iTeX is full LaTeX-compatible. Jacques Distler’s aim is that it should be as compatible as possible, but there are a few things that predate his incumbency and cannot be removed without breaking backward-compatibility. One of the most obvious of these is the \array command. The reasons why this is a problem are:

1. There is an \array command in LaTeX, but it is not what \array is used for in iTeX. The \array command in LaTeX is actually a synonym for \begin{array} so the contents of the array (in LaTeX) is what follows the command rather than an argument to it.
2. For some reason, people on the nLab have adopted the \array command for aligning stuff.

This means that when exporting an nLab page, \array breaks the compilation. Fortunately, there is a relatively simple solution.

### Immediate Solution

After exporting the page, use a text editor to replace all occurrences of \array by something safe like \itexarray. Then add the following code in the preamble:

\newcommand{\itexarray}[1]{\matrix #1 \endmatrix}


### Long-term Solution

Whenever you come across the \array construction in an nLab page, replace it by \begin{matrix} ... \end{matrix}.

Note that the \array command makes use of the fact that arrays in MathML are a little different to arrays in LaTeX so there are occasions that these extras are used and those situations should not be changed. But if none of these are used, it’s safe to replace \array by the matrix environment. For more on the difference, see this page on the iTeX version.

(That page might also be the source of why \array appears so much in nLab pages as there is an example there of a commutative diagram which probably got cut-and-pasted in to the first commutative diagram on the n-Cafe!)

• CommentRowNumber2.
• CommentAuthorMike Shulman
• CommentTimeOct 5th 2010

Wouldn’t a better long-term solution be to modify the TeX output feature of instiki so that it translates \array into something like \itexarray itself? No one is going to be writing \array in iTeX and wanting it to come out as the LaTeX version.