A closed form of hbim. (Contributed by NM, 2-Jun-1993.)
\( \vdash (\varphi \rightarrow \psi) \rightarrow \forall x \, (\varphi \rightarrow \psi) \)
\( \vdash (\varphi \rightarrow \psi) \rightarrow \varphi \rightarrow \forall x \, \psi \)
\( \vdash \forall x \, (\varphi \rightarrow \psi) \leftrightarrow \varphi \rightarrow \forall x \, \psi \)