Extensive form notation in game theory

Question

I'm struggling to understand the notation surrounding an extensive form game. I've taken this example from the Wikipedia page for subgame-perfect equilibrium.

So for this game: subgame example I don't understand the matrix notation (given on the Wiki page - can't post more than two images...). Does (K,K) mean player 1 chooses K, then sees player 2s choice and decides to stick with K? If so, shouldn't L (K,U) be (1,3)?

Thanks

Answer 1

Actually, $(K,K)$ refers to Player 2, not Player 1. The convention for the normal form (what you call matrix form) is that 1 picks rows, and 2 picks columns.

The notation $(a,b)$ indicates what Player 2 plays in each of her two decision nodes; namely, $a$ in $2_1$ and $b$ in $2_2$. In your specific case, $(K,K)$ means that Player 2 always plays $K$. The notation $(K,U)$ would say that she plays $K$ in $2_1$ and $U$ in $2_2$.