Check out my books on Amazon (paid link): https://amzn.to/2SiQjlp Let's play a game of face card poker. You begin by receiving a face-down card from a standard deck of playing cards. Face cards are winning cards; non-face cards are losing cards. After privately looking at it, you bet either $2 or $5. Your opponent sees your bet but not your card and chooses whether to fold or raise. If they fold, then they pay you money equal to your bet. If they raise, what happens next depends on the card. If it is a face card, they must pay you double your bet. If it is a non-face card, you must pay them double your bet. How should you play this game? Perfect Bayesian equilibrium may provide some help...