X-Git-Url: http://gitweb.michael.orlitzky.com/?p=mjotex.git;a=blobdiff_plain;f=mjo-arrow.tex;h=9bf9dc5555515e45f2a98b25d5c89310375d3b03;hp=75b70c9d8b3670d94fb5ed5ca953d20b2464a008;hb=f9205a3b883c08499edfdd3f9d1a6170a6fc6755;hpb=d85706cc1efea350df9e957f6583a92d4e05359f

diff --git a/mjo-arrow.tex b/mjo-arrow.tex
index 75b70c9..9bf9dc5 100644
--- a/mjo-arrow.tex
+++ b/mjo-arrow.tex
@@ -1,6 +1,27 @@
 %
 % Things dealing with arrows in a category. Or functions, basically.
 %
+\ifx\havemjoarrow\undefined
+\def\havemjoarrow{1}
+
+
+\input{mjo-common} % for \of, at least.
+
+\ifx\operatorname\undefined
+  \usepackage{amsopn}
+\fi
+
+
+% The constant function that always returns its argument.
+\newcommand*{\const}[1]{\operatorname{const}_{{#1}}}
+
+\ifdefined\newglossaryentry
+  \newglossaryentry{const}{
+    name={\ensuremath{\const{a}}},
+    description={the constant function that always returns $a$},
+    sort=c
+  }
+\fi
 
 % The identity operator/arrow on its argument.
 \newcommand*{\identity}[1]{ \operatorname{id}_{{#1}} }
@@ -11,3 +32,9 @@
 
 % 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} }
+
+
+\fi