Add the \preimage macro.

diff --git a/examples.tex b/examples.tex
index 98ddfd550b08ea4fd78301eb47c0aea19cb8de7a..e0ffcb97a11ce5a97a2e837e7c994fd19714e1ae 100644 (file)
--- a/examples.tex
+++ b/examples.tex
@@ -28,7 +28,8 @@
   \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}

diff --git a/mjo-arrow.tex b/mjo-arrow.tex
index 75b70c9d8b3670d94fb5ed5ca953d20b2464a008..8b44ded1753eb175124ed71fa73ad4e5ec9b35e5 100644 (file)
--- a/mjo-arrow.tex
+++ b/mjo-arrow.tex
@@ -2,6 +2,8 @@
 % Things dealing with arrows in a category. Or functions, basically.
 %
 
+\input{mjo-common}
+
 % The identity operator/arrow on its argument.
 \newcommand*{\identity}[1]{ \operatorname{id}_{{#1}} }
 
@@ -11,3 +13,6 @@
 
 % The inverse of an arrow, function, or whatever.
 \newcommand*{\inverse}[1]{ #1^{-1} }
+
+% The preimage of the second argument (a set) under the first (a function).
+\newcommand*{\preimage}[2]{ #1^{-1}\of{#2} }