let's try not to make those macro names too long

docs/iris.sty

@@ -167,7 +167,7 @@
 \newcommand{\mcore}[1]{{\mid}#1{\mid}} % using "|" here makes LaTeX diverge. WTF.
 \newcommand{\mnocore}{\bot}
 \newcommand{\mtimes}{\mathbin{\cdot}}
-\newcommand{\mundefined}{\lightning}
+\newcommand{\mundef}{\lightning}
 
 \newcommand{\mupd}{\rightsquigarrow}
 \newcommand{\mincl}[1][]{\ensuremath{\mathrel{\stackrel{#1}{\preccurlyeq}}}}
@@ -391,7 +391,7 @@
 \newcommand{\Auth}{\textsf{Auth}}
 
 % Sum
-\newcommand{\csumm}{\mathrel{+_{\!\mundefined}}}
+\newcommand{\csumm}{\mathrel{+_{\!\mundef}}}
 \newcommand{\cinl}{\textsf{inl}}
 \newcommand{\cinr}{\textsf{inr}}