fix spacing for \seen

papers/icfp2021/notations.tex

@@ -297,7 +297,7 @@
 \newcommand{\valid}[1]{\mathit{valid}\,#1}
 
 % the “seen” predicate:
-\newcommand{\seen}{\uparrow\!}
+\newcommand{\seen}{\mathop\uparrow\!\!\:}
 %\newcommand{\seen}{\mathop{\text{\eye}}}   % requires package <dingbat>
 %  \let\checkmark\undefined
 %  \usepackage{dingbat}