New Scientist Enigma 515 – Foreign Ties
by Susan Denham
From Issue #1667, 3rd June 1989
The Anglo-Slovak club had its meeting last week. Those present were Tom, Vyctur, Ted, Tago, Ray, Min, Wex, Olav, Russ and Cy.
Some of the members stood up and took part in an old Slovakian dance, rather like a Morris dance. The dancers stood around the floor with no three in a straight line and between each pair a taut piece of ribbon was stretched across the ﬂoor. Some ribbons were pink and the rest were blue. I noticed that there was a pink ribbon between two of them precisely when their Christian names had an odd number of letters in common (So, for example, had a Jane, David and Victor been dancing, there would have been a pink ribbon from Jane to David, a blue from David to Victor, and a blue from Jane to Victor.) As soon as I saw how many dancers there were, I realised that two of the ribbons would have to cross. But they had arranged themselves in such a way that there was no pink and no blue triangle of ribbons.
Who was dancing?