Template page

This page is meant to provide a general example and template for new nLab-pages. You can look at its source code to see how the various parts are done. A minimal template is given first which can be copy-and-pasted into newly created pages. See HowTo for more details.

category: meta

Minimal Template Code

# Contents (or put a title here)
* this block creates the table of contents, leave as is
{: toc}

## Idea


## Definition 


## Properties


## Examples


## References


A more detailed example follows. Check out the source code here to see how it’s coded:



It is an old observation that xyz. One notices that from the nPOV this is just an abc. This leads to the definition of a uvw. It is useful for doing klm and provides the basis for the more general theory of äöü.


A uvw is effectively a uv together with a w. Its main property is encoded in Somebody’s Theorem which says that it consists of precisely three letters. The archetypical example of a uvw is μνω\mu \nu \omega; details will be explained in the special examples paragraph.


As Jacques Distler said,

See more about definition/theorem/proof-environments.



A uvw is a UVW in which all letters are lower case.

This may be summed up in the slogan:

A uvw is just what it looks like.



Every uvw (Def. ) contains at least one letter.


By inspection.


Every uvw contains strictly more than one letter.


Use the above lemma and continue counting:

(1)1+1=2. 1 + 1 = 2 \,.


Every uvw (Def. ) contains exactly three letters.


Along the lines of the above proposition, we use equation (1) and then conclude with

2+1=3. 2 + 1 = 3 \,.

Notice that this is indeed independent of in which order we sum up the letters, in that the following diagram commutes:

×× Id×+ × +×Id + × + . \array{ \mathbb{N}\times \mathbb{N} \times \mathbb{N} & \overset{Id \times + }{\longrightarrow} & \mathbb{N} \times \mathbb{N} \\ {}^{\mathllap{+ \times Id}} \big\downarrow && \big\downarrow^{\mathrlap{+}} \\ \mathbb{N} \times \mathbb{N} & \underset{+}{\longrightarrow} & \mathbb{N} } \,.


No uvw contains more than three letters.


Special cases

  • First case

  • Second case

  • Third case

First person: I listed all of the special cases that I know above, but didn't Grothendieck study an important version too?

Second person: No, you're thinking of Lawvere. When I find the reference, I'll put it here.

Specific examples

For ease of reference, we will number the examples.

  1. The first example is obvious.

  2. The second example is a slight variation of (1).

  3. The third example is completely different from either (1) or (2).


The original definition appeared in section 3 of

Last revised on March 18, 2021 at 01:18:48. See the history of this page for a list of all contributions to it.