I have a question about this propositional logic question.
I understand that Hypothetical syllogism confirms that an argument with the form (below) makes sense:
$1.$ P$\to$Q
$2.$ Q$\to$R
hence, P$\to$R
but how would you make a natural deduction proof for the argument with a bi-conditional and a conditional premise such as: $1.$ P$\leftrightarrow$Q $2.$ Q$\to$R hence, P$\to$R