Create semi-simplicial type

- The basic syntax is extended Markdown.
- Links to other nLab pages should be made by surrounding the name of the page in double square brackets: [[ name of page ]]. To link to an nLab page but show a different link text, do the following: [[ name of page | link text to show ]].
- LaTeX can be used inside single dollar signs (inline) or double dollar signs or \[ and \], as usual.
- To create a table of contents, add \tableofcontents on its own line.
- For a theorem or proof, use \begin{theorem} \end{theorem} as you would in LaTeX. Labelling and referencing is exactly as in LaTeX, with use of \label and \ref. The full list of supported environments can be found in the HowTo.
- Tikz can be used for figures almost exactly as in LaTeX. Similarly, tikz-cd and xymatrix can be used for commutative diagrams. See the HowTo.
- As an alternative to the Markdown syntax for sections (headings), one can use the usual LaTeX syntax \section, \subsection, etc.
- For further help, see the HowTo, or you are very welcome to ask at the nForum.

Please make some comments about the new page, such as a brief summary of its contents, how it relates to other pages (existing or future), and how it might be further developed. They will form the first comment of a thread at the nForum for discussing this page.