The Trebuchet

In an all-parent encounter last week, the players stumbled upon this position, known as the Trebuchet. A trebuchet is a big wooden catapult, and its connection with this position is not known, except that it may catapult a player from joy to despair... Normally, it's an advantage for it to be your turn so you can get on with your plan, but in this position, whoever has to move next, loses! Can you see how? The situation of an unhappy forced move is called Zugzwang; it's not ever so common but more unusual is this situation where BOTH sides are in Zugzwang. P.S. Interested in this sort of thing? Here are some more: http://exeterchessclub.org.uk/content/simplest-mutual-full-point-zugzwangs