Ko threat in seki example
Let us consider this position as a source of ko threats.
First assume Black is to play. How many ko threats does Black have here?
Black can play --- as a long threat. Since is atari, stopping there isn't good for a small ko. And for a large ko the threat of , to make six points, isn't interesting.
Note that Black neither gains nor loses points here.
Is therefore this position an example of a double ko threat? White has one threat here worth over 20 points. Black can get two lesser threats. In a small ko White will remove this double threat. Black can theoretically remove it, too (cf. slightly different example at unremovable ko threat). In a larger ko White will have no reason to remove the threat, and Black's plays to remove the threat may instead be gote.
This is therefore a more complex example for the remove double threats before you first capture the ko heuristic.