I have a question. Given a biconditional statement of the following form:

> 
> Show $p$ if and only if $q$ or $s$.
> 
> 
> 

I was confused as to how to proceed.

In one direction of assuming $p$ is true, is it suffice to show $q$ is true? Or do I also need to consider if $p$ holds, then $s$ is true? 

For the other direction, do I need to show two things: Assume $s$ is true and deduce $p$ and also assume $q$ and deduce that $p$ is true? 

Thanks for the clarification.