Editing Help:Editing (section)

===Math===

==== Under/overbrace ====

{| border=1
| Wikipedia's new under/overbrace syntax
| <nowiki><math>\underbrace{2+3}_5</math></nowiki>
| <math>\underbrace{2+3}_5</math>
| works here in a different way.
|-
| The former Wikipedia syntax
| <nowiki><math>\begin{matrix} \underbrace{2+3} \\5 \end{matrix}</math></nowiki>
| <math>\begin{matrix}\underbrace{2+3}\\5\end{matrix}</math>
| works here as expected
|}

The former syntax uses matrix environment as an auxiliary tool — the same  tool can be used to typeset matrices:
:<nowiki><math>\left[ \begin{matrix}1 & 2 \\ 3 & 4\end{matrix} \right]</math></nowiki>
:<math>\left[ \begin{matrix}1 & 2 \\ 3 & 4\end{matrix} \right]</math>

Multiple-embedded underbracings
:<math>\begin{matrix}1+\underbrace{2+3}\\\underbrace{\;\;\;\;\;\;\;\;\;5\;\;\;}\\6\end{matrix}</math>
can be achieved with the subscript-using syntax of the new Wikipedia in a straightforward way — embedding the parts in a hierarchical way.

As for the matrix-using syntax of the former Wikipedia and recent Haskell Wiki, a similar idea may work too, because also the <nowiki>\begin{matrix}...\end{matrix}</nowiki> environments can be embedded in a hierarchical way:
:<nowiki><math>\left[ \begin{matrix}1 & 2 \\ 3 & \left[ \begin{matrix} 4 & 5 \\ 6 & 7\end{matrix} \right] \end{matrix} \right]</math></nowiki>
:<math>\left[ \begin{matrix}1 & 2 \\ 3 & \left[ \begin{matrix} 4 & 5 \\ 6 & 7\end{matrix} \right] \end{matrix} \right]</math>
thus, also underbracings can be embedded, but precise alignment must be achieved with care.

There is also an alternative way to achieve the same visual result, using a rather "nasty" (but easy) trick
:<nowiki><math>\begin{matrix}1+\underbrace{2+3}\\\underbrace{5}\\6\end{matrix}</math></nowiki>
it is almost good
:<math>\begin{matrix}1+\underbrace{2+3}\\\underbrace{5}\\6\end{matrix}</math>
but the precise alignment must be made by hand, e.g.
:<nowiki><math>\begin{matrix}1+\underbrace{2+3}\\\underbrace{\;\;\;\;\;\;\;\;\;5\;\;\;}\\6\end{matrix}</math></nowiki>
resulting the expected
:<math>\begin{matrix}1+\underbrace{2+3}\\\underbrace{\;\;\;\;\;\;\;\;\;5\;\;\;}\\6\end{matrix}</math>
Thus, this is a rather nasty trick, operating at a low level and failing to grasp the logical structure. But it has an easy (layered) structure.
 
==== Some new math symbols ====

Upper corner quotation marks are used often in mathematical logic to denote "quotation", stressing that the enclosed expression is meant as literal part of the object language. In LaTeX's mathematical mode environments, they can be typeset with <nowiki>\ulcorner</nowiki> and <nowiki>\urcorner</nowiki>. The recent Wikipedia knows this solution too. In the former Wikipedia and recent Haskell Wiki, this solution does not work, another notation must be chosen or the sign must be inserted as an image.