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# Biconditional introduction

The biconditional means if $P$ is the case, $Q$ must be the case and if $Q$ is
the case, $P$ must be the case. Thus to introduce this operator we must
demonstrate both that $Q$ follows from $P$ and that $P$ follows from $Q$. We do
this via two sub-proofs.

![](/img/bi-intro.png)