### Hypertext Help with LaTeX

# \stackrel

This can be used to stack something above something else; used in math mode.

`\stackrel{top}{bot}`

The first argument, `top`, is typset immediately above the
second argument, `bot`; the former is set in the same
math style as a superscript.
For example

`H$_2$CO$_3$ $\stackrel{\rm heat}
{\longrightarrow}$ H$_2$O + CO$_2$`

will produce something like
`
heat
H CO ------> H O + CO
2 3 2 2
`

Note that the the `\rm` declaration is used
so that "heat" is set in Roman face and not math italics.
This command does not seem to be well documented but appears to work,
at least in current versions of LaTeX 2.09.

The argument is considered to be a single variable
sized math symbol for purposes of placing limits below
(subscripts) and above
(superscripts) in
display math style. For example,

`\mathop{\sum \sum}_{i,j=1}^{N} a_i a_j`

would produce something like
N
--- ---
\ \
/ / a a
--- --- i j
i,j

It is possible to create **two rows** of "subscripts" by using
a similar construction: The first row is created as subscripts of the symbol
in the usual way and a lower row is created by placing this whole construct
as the argument of a `\mathop` command with its own subscript. For
example
`\mathop{\sum_{i,j=1}^{N}}_{i>j}`

would produce something like
N
---
\
/
---
i,j=1
i>j

Related topics
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Revised: Sheldon Green, 15 Aug 1995.