As I've mentioned, giving tokens of appreciation is a major Singaporean pastime, and for once I was ready. This was for the students I've been mentoring, who want to continue for a few more months too. I gave them a set of ball bearings and magnetic rods good for modest structure-building, and a cube with plastic rods one can slide along the surface, to tie or untie knots on the strings within. Their token to me was a plastic battery-powered turtle which rattles around; and a book of Sudoku puzzles. Sudoku is a magic square/crossword puzzle mix, a nine-by-nine grid, and in each row, each column, and each of nine three-by-three sub-squares, each numeral from 1 to 9 is used exactly once. A set of starting numbers are given and the challenge is to place the rest.
It may seem ironic, but I don't care for these sorts of logic puzzles, and I'm not sure I believe my reason. My feeling is while I can work a Sudoku out -- or those similar puzzles where you're given eight clues and have to figure out who owns which animal, who owns which method of transportation, and which stayed in the building which day -- is that even if you excel in solving these puzzles, you don't get any useful skills other than solving these puzzles. In contrast deriving the trigonometric identities from the integral definition of the arc-sine function, yeah, teaches you a lot about that particular task, but it also gives side training in all sorts of integral, differentiation, and sequence- and series-trick usable in unrelated fields.
But I don't quite believe myself, since there are many things I do that have no other use, like my grand strategy game sideline. All I learn playing Hearts of Iron is how to play Hearts of Iron. Maybe I'm just evading the crossword-puzzle fanaticism my grandfather had.
Trivia: Benjamin Franklin created a magic square so that: each row adds to 260 but stopping halfway adds to 130; any four squares equally distant from the center or corners adds to 130; any four-element diagonal starting from the lower left edge, going up to the center, then going diagonally down to the right adds to 260; the four corners plus four center pieces adds to 260; and any two-by-two sub-square adds to 130. Source: Life Science Library: Mathematics, David Bergamini.
Currently Reading: The Sputniks Crisis and Early United States Space Policy, Rip Bulkeley.