\begin{section}{Arrow}
The identity operator on $V$ is $\identity{V}$. The composition of
$f$ and $g$ is $\compose{f}{g}$. The inverse of $f$ is
- $\inverse{f}$.
+ $\inverse{f}$. If $f$ is a function and $A$ is a subset of its
+ domain, then the preimage under $f$ of $A$ is $\preimage{f}{A}$.
\end{section}
\begin{section}{Common}
The function $f$ applied to $x$ is $f\of{x}$. We can group terms
like $a + \qty{b - c}$ or $a + \qty{b - \sqty{c - d}}$. Here's a
set $\set{1,2,3} = \setc{n \in \Nn[1]}{ n \le 3 }$. Here's a pair
- of things $\pair{1}{2}$ or a triple of them
- $\triple{1}{2}{3}$. The Cartesian product of two sets $A$ and $B$
- is $\cartprod{A}{B}$; if we take the product with $C$ as well,
- then we obtain $\cartprodthree{A}{B}{C}$. The direct sum of $V$
- and $W$ is $\directsum{V}{W}$ and the factorial of the number $10$
- is $\factorial{10}$.
-
+ of things $\pair{1}{2}$ or a triple of them $\triple{1}{2}{3}$,
+ and the factorial of the number $10$ is $\factorial{10}$.
+
+ The Cartesian product of two sets $A$ and $B$ is
+ $\cartprod{A}{B}$; if we take the product with $C$ as well, then
+ we obtain $\cartprodthree{A}{B}{C}$. The direct sum of $V$ and $W$
+ is $\directsum{V}{W}$. Or three things,
+ $\directsumthree{U}{V}{W}$. How about more things? Like
+ $\directsummany{k=1}{\infty}{V_{k}} \ne
+ \cartprodmany{k=1}{\infty}{V_{k}}$. Those direct sums and
+ cartesian products adapt nicely to display equations:
+ %
+ \begin{equation*}
+ \directsummany{k=1}{\infty}{V_{k}} \ne \cartprodmany{k=1}{\infty}{V_{k}}.
+ \end{equation*}
Here are a few common tuple spaces that should not have a
superscript when that superscript would be one: $\Nn[1]$,
$\Zn[1]$, $\Qn[1]$, $\Rn[1]$, $\Cn[1]$. However, if the
(indexed) union and intersections of things, like
$\unionmany{k=1}{\infty}{A_{k}}$ or
$\intersectmany{k=1}{\infty}{B_{k}}$. The best part about those
- are that they do the right thing in a display equation:
+ is that they do the right thing in a display equation:
%
\begin{equation*}
\unionmany{k=1}{\infty}{A_{k}} = \intersectmany{k=1}{\infty}{B_{k}}
\end{equation*}
- %
\end{section}
\begin{section}{Cone}
The set of all bounded linear operators from $V$ to $W$ is
$\boundedops[W]{V}$. If $W = V$, then we write $\boundedops{V}$
instead.
+
+ The direct sum of $V$ and $W$ is $\directsum{V}{W}$, of course,
+ but what if $W = V^{\perp}$? Then we wish to indicate that fact by
+ writing $\directsumperp{V}{W}$. That operator should survive a
+ display equation, too, and the weight of the circle should match
+ that of the usual direct sum operator.
+ %
+ \begin{align*}
+ Z = \directsumperp{V}{W}\\
+ \oplus \oplusperp \oplus \oplusperp
+ \end{align*}
+ %
+ Its form should also survive in different font sizes...
+ \Large
+ \begin{align*}
+ Z = \directsumperp{V}{W}\\
+ \oplus \oplusperp \oplus \oplusperp
+ \end{align*}
+ \Huge
+ \begin{align*}
+ Z = \directsumperp{V}{W}\\
+ \oplus \oplusperp \oplus \oplusperp
+ \end{align*}
+ \normalsize
\end{section}
\begin{section}{Listing}
The interior of a set $X$ is $\interior{X}$. Its closure is
$\closure{X}$ and its boundary is $\boundary{X}$.
\end{section}
-
+
\end{document}