Distribution of implication with conjunction. (Contributed by NM,
31-May-1999.) (Proof shortened by Wolf Lammen, 6-Dec-2012.)
\( \vdash \varphi \rightarrow \psi \rightarrow \chi \leftrightarrow \varphi \wedge \psi \rightarrow \varphi \wedge \chi \)
\( \vdash \varphi \rightarrow \psi \rightarrow \chi \leftrightarrow \varphi \rightarrow \psi \rightarrow \varphi \wedge \chi \)
\( \vdash \varphi \wedge \psi \rightarrow \varphi \wedge \chi \leftrightarrow \varphi \rightarrow \psi \rightarrow \varphi \wedge \chi \)