Double check

What do you move in figure. 1?

 figure. 1

In fact, you can mate the opponent's King in one move, +R-2d (figure. 2).
This is so-called "Double check." In figure. 2, the opponent's King can't escape anywhere. If the opponent put pieces between King and one of Rook and Horse and stop the influence of it, I can take the King by the other.
Occasionally, Double check is so powerful technique.

figure.2

The below kifu of Central Rook is famous for very short game by double check.



The gote should have defend in 10th move (figure. 3) by such as K-4b instead of P-8e.
However, some players don't notice the mate by Rx3c+ in the position of  figure. 3, so you can try it if you have a chance.

figure. 3