Hi Dmitri, I am not sure what you were attempting, but I have modified the entry now to use more or less exactly this code, and it works fine. Double dollars should have a blank line before and after; maybe that was the cause of the problems you ran into. Itex2MML didn’t seem to like the `\,`

inside the `\mathrm`

, so I just added some space in a different way.

The MathOverflow code is this one:

```
$$P(i,j;k) = \begin{cases} \mathbb{Z} & \mathrm{if\,\,} i+j=k, \\
\mathbb{Z} \oplus \mathbb{Z} & \mathrm{if\,\,} i+j=k+1, \\
\mathbb{Z} & \mathrm{if\,\,} i+j=k+2, \\
0 & \mathrm{else}.
\end{cases}$$
```

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If you give me a pointer to the code on MO, I’ll try to convert it.

]]>Trying to resolve a problem with mysteriously disappearing text after a displayed formula $$ … $$.

Appears to be a parser bug.

]]>Copied a MathOverflow answer about tensor products as Day convolutions.

Unable to make the \begin{cases} … \end{cases} work. \array and \begin{aligned} do not work either.

The error messages are meaningless, I am giving up after several attempts.

]]>following public demand, I added to *tensor product of chain complexes* a detailed elementary discussion of the tensor product $I_\bullet \otimes I_\bullet$ of the (normalized) chain interval with itself, and how it gives chains on the cellular square: in *Square as tensor product of interval with itself*.