\newcommand{\eqn}[2]{ #2 \tag*{\mbox{#1}} }
-\newcommand{\bigforall}{\mathop{\hbox{\huge$\forall$}}}
+%\newcommand{\bigforall}{\mathop{\hbox{\huge$\forall$}}}
+\newcommand{\bigforall}{%
+ \mathop{\mathchoice%
+ {\hbox{\huge$\forall$}}%
+ {\hbox{\Large$\forall$}}%
+ {\hbox{\normalsize$\forall$}}%
+ {\hbox{\scriptsize$\forall$}}}%
+}
\begin{document}