I am reviewing MIT 18.440 slides. I am wondering why the question that is worded as How many bridge hands have at most two suits represented? has a given answer of ${4\choose 2}{26 \choose 13} - 8$.
I understand that the ${4\choose 2}$ takes in account choosing the two suits that the hand will have, and ${26 \choose 13}$ indicates we're choosing 13 cards out of a limited subset of the 52 total cards.
But I'm not sure where the extra $-8$ comes from. Does it include special cases such as the 4 hands that have all 13 cards from one suit?
Possible question to use as reference: A bridge hand void in one suit