The rules

1. Both players hold the same thirteen cards, ace through king. A third set of thirteen is shuffled and becomes the prizes.
2. One prize is turned face up. Both players bid one card from their hand, in secret.
3. The bids are revealed together. The higher bid takes the prize, worth its own rank in points.
4. Both bids are spent either way, whether they won the prize or not.
5. Equal bids win nothing: the prize rolls over and joins the next one, so the following round is worth both.
6. Thirteen rounds and the hands are empty. The most points wins.

Everything is public except a bid that has not been revealed yet, including exactly which cards your opponent has already spent. Keeping track of what is left in their hand is the whole game. Ties rolling over is one of three published ways to handle them, chosen because discarding the prize makes a tie dull and splitting it produces fractions.