In checkless chess it’s illegal to give check without giving checkmate. This changes the whole complexion of the game. T.R. Dawson published this example in Die Welt in 1951. White is to mate in two moves.

The answer, 1. f6, threatens 2. Qf5, which strangely is mate because the black king can’t move off the long light diagonal, since that would discover check by the black bishop without giving checkmate. Black can try to prevent this finish by playing 1. … Qc8, guarding f5 and thus making 1. Qf5 itself illegal. But this permits 2. Nxd6, which now is mate because the black king has nowhere to run on the long diagonal and 2. … cxd6 is illegal because this would give a mateless check.

Similarly, if Black tries to stop 1. Qf5# with 1. … Qxf6, then 2. Nc5 is mate because Black can’t capture the knight — again, this would expose White’s king to an illegal check. And if Black tries to answer White’s first move with 1. … d5, to block the long light diagonal and free his king to flee elsewhere, then White can play 2. Qe5#, an ordinary (and legal) mate.

The Royal Statistical Society’s 2024 Christmas Quiz consists of two parts, a warmup section and the quiz itself, each consisting of 12 questions. Solvers (and teams) have until January 5 to submit their solutions, and the top three entrants will win a donation of £150, £120, or £90 to the charity or good cause of their choice. Updates and corrections will be posted on the competition website, and solutions will be published in January, together with the names of the winners.

In January 1984, Games magazine challenged its readers to create a form of communication in which a positive statement can be changed to a negative one solely by changing its punctuation. As an example, contributing editor Gloria Rosenthal offered this love letter:

Dear John:

I want a man who knows what love is all about. You are generous, kind, thoughtful. People who are not like you admit to being useless and inferior. You have ruined me for other men. I yearn for you. I have no feelings whatsoever when we’re apart. I can forever be happy — will you let me be yours?

Harriet

How can Harriet tell John to get lost solely by repunctuating her letter?

A puzzle by S. Dvoryaninov from the July-August 1994 issue of Quantum:

A very large military band marched in square formation on a parade ground, then regrouped into a rectangle so that the number of rows increased by 5. How many musicians were in the band?

The 2024 GCHQ Christmas Challenge is now live. Devised by Government Communications Headquarters, the British intelligence agency, this year’s puzzles encourage children aged 11-18 to think laterally and work as a team, testing skills including codebreaking, mathematics, and lateral thinking. “This year for the first time there are three additional elements hidden within the card for those who want to take on an extra challenge.”

The agency has included puzzles in its Christmas cards to global national security heads since 2015. Director Anne Keast-Butler said, “The puzzles are aimed at teenagers and young people, but everyone is encouraged to give them a try — they might surprise you.”

Fleeing a rainstorm in 1710, Joseph Addison took shelter at an unfamiliar house. “As I sat in the porch, I heard the voices of two or three persons, who seemed very earnest in discourse. My curiosity was raised when I heard the names of Alexander the Great and Artaxerxes; and as their talk seemed to run on ancient heroes, I concluded there could not be any secret in it; for which reason I thought I might very fairly listen to what they said.”

After several parallels between great men, which appeared to me altogether groundless and chimerical, I was surprized to hear one say, that he valued the Black Prince more than the duke of Vendosme. How the duke of Vendosme should become a rival of the Black Prince’s, I could not conceive: and was more startled when I heard a second affirm with great vehemence, that if the emperor of Germany was not going off, he should like him better than either of them. He added, That though the season was so changeable, the duke of Marlborough was in blooming beauty. I was wondering to myself from whence they had received this odd intelligence, especially when I heard them mention the names of several other great generals, as the prince of Hesse, and the king of Sweden, who, they said, were both running away. To which they added, what I entirely agreed with them in, that the crown of France was very weak, but that the mareschal Villars still kept his colours. At last one of them told the company, if they would go along with him, he would shew them a chimney-sweeper and a painted lady in the same bed, which he was sure would very much please them.

What explains this strange conversation?

This year’s puzzle Christmas card from Chalkdust Magazine, designed by Matthew Scroggs, contains 10 puzzles. Answering them correctly will guide you in completing a Christmas-themed picture. Here’s a printable PDF.

And King William’s College has released its annual general knowledge quiz, which appears as fiendish as ever. (“During 1924, in what could one learn of the ordinariness of Chandrapore?”) MetaFilter is sponsoring a shared Google Sheet where solvers can collaborate; answers will appear on the Guardian website on January 15.

A problem from the January-February 1991 issue of Quantum:

Prove that the area of the yellow rectangle is half that of the full octagon.

Thomas Taverner published this remarkable problem in the Dubuque Chess Journal in 1889. White is to mate in two moves.