---
tags:
  - logic
---

# 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)
