"Richmond will win the AFL premiership only if pigs can fly"

Here is how ive gone about doing this:

if p="pigs can fly" and r="Richmond will win the AFL premiership"

then the above statement can be written as p-->r

converse: (-p)-->(-r) If pigs can't fly, Richmond will not win the AFL premiership.

contrapositive: (-r)-->(-p) If Richmond do not win the AFL premiership then pigs cannot fly

Is what I have done correct? The answers given suggest otherwise, but I'm convinced that I haven't made a mistake. Can anyone clarify this?