Competition Problem 137b
South to make seven spades. West leads the ♦Q.
Successful solvers: Alexander Baranovitch, Steve Bloom, Ian Budden, Ankush Mandal, Leigh Matheson, Radu Mihai, Sebastian Nowacki, Prahalad Rajmukar, A.V. Ramana Rao, Zoran Sibinović, F.Y. Sing, Andries van der Vegt, Dick Yuen, Wim van der Zijden Tables
South wins with the ♦A and leads the ♣J, covered by West and ruffed by North, who leads the ♥J, covered by East and ruffed by South, who leads the ♣10, covered by West and ruffed by North, who leads the ♥10 … and this process continues until this position is reached with South on lead:
South runs the remaining spades for a simultaneous double squeeze. On the last spade West has to discard a diamond to keep a guard against North’s heart loser, so North discard that loser and East is squeezed in the minor suits.
The cross-ruffing in clubs and hearts has the effect of transferring the guard in each of those suits, from one defender to the other. Woe betide any writer who calls it “transferring the menace” or “isolating the guard”. The menaces, so called because they threaten to win a trick if the suit is discarded from by the opposition, are North’s low hearts and South’s low club, and they are so throughout the play. Isolating a guard refers to, for example, what happens in the above ending when West is forced to discard a diamond, isolating the guard in that suit in the East hand. It can happen in preliminary play when declarer holds something like Ax opposite Kxxx, when three rounds of the suit, South ruffing the third, leaves one opponent in sole control of the suit.
Note added May 13th 2019: My authoritarian comment on the terminology has been challenged by “Ryou Niji” (a pseudonym). An alternative viewpoint is that the property of being a menace card in the above example has been transferred from one card (say the ♣J or ♥J) to another of the same suit in the same hand (say the ♣4 or ♥4). In that case both guard and menace are transferred, but in different senses of that word. I suppose one could add “and the menace from one card to another” to the first sentence of the paragraph above, but I wouldn't want to mention that point without also mentioning the guard transfer.
See the solution to Competition Problem #4 for the recommended tabular format if you prefer not to write in English prose.
Hugh Darwen, 2016