WHO IS TELLING THE TRUTH?
KENDRA says (she said this when she came back from the bathroom at 8:38pm and read the puzzle): Brad is a truth-teller.
kendra figured the original puzzle out in seven minutes which is faster than I did the first time I solved a Smullyan one this hard, she said it was good and that I should add her as a fourth speaker and make it harder so she could solve a bigger one next Friday — so here she is, the puzzle is now four-statement, the new solution is the same as the old plus Kendra = TRUTH-TELLER because she really did say I am a truth-teller and she is not lying about it — but for the puzzle to still have exactly one solution the way Smullyan would want it, I had to add this rule too: at least one of the four speakers is a fibber AND at least one is a truth-teller.
— B.S., February 13 1987, the next Friday, before Scrabble starts at 7:14pm.
1.
ERIC says: Stacy is a fibber.
2.
STACY says: Mr. Tibbs and I are not both truth-tellers.
3.
MR. TIBBS says (via squeak): Eric is a truth-teller.
deduction work →
casetells?ok?
if Eric tells truth → Stacy fibs → her stmt false → both Stacy AND Tibbs are truth-tellers → but Stacy is a fibber → contradicts
so Eric fibs → so Stacy is NOT a fibber → so Stacy tells truth → her stmt true → Tibbs & Stacy not both truth → so Tibbs fibs
check 3: Tibbs fibs, so "Eric is truth" is false, so Eric fibs ✓ consistent
KIDS WHO SOLVED THIS:
2
Eric was telling Greg Schimanski at the pencil sharpener that Mr. Tibbs hadn't moved in his cage all morning and looked sick — I wrote this down in my comp-book during silent reading. Eric says this kind of stuff a lot but he is hard to read because sometimes he is being funny and sometimes he is being serious and the puzzle had to be solvable either way so I had to set it up so that whether Eric is a truth-teller or a fibber, you can still work it out.
Stacy said this exact sentence at recess Tuesday — Mr. Tibbs spins on his wheel. A whole class of kids leans in. My sister steps quietly back. I wrote the not-both form because the plain form would collapse the case-tree too fast, and Smullyan would say a fair puzzle needs the disjunction to do real work — the "or" is what forces you to check Tibbs separately instead of skipping ahead.
For the third statement I needed Mr. Tibbs to actually say something and he is a hamster so this took some thinking — Mrs. Helquist holds the sunflower seed and asks the question and Tibbs squeaks once for yes and twice for no, which is something the class agreed on in September. On Tuesday she asked Tibbs if Eric was telling the truth about him being sick and he squeaked once. Stacy translated. I am writing the statement as a positive yes because that is what the squeak meant in the room.
Eric Pitlik sits two desks behind me in row 3. His dad works at the Allen-Bradley plant in Pewaukee like our friend Kyle's dad. Eric is good at four-square but he is not in Math Olympiad — Mr. Kowalczyk asked him in October and he said no thank you which was fine, not everyone has to want to do it. Eric let me borrow his magnifying glass once for a whole week.
Stacy Voorhees is the second-best math student in our class after me — she got a 94 on the November math test and I got a 97. She is also in Math Olympiad and she is the one who told Mr. Kowalczyk about Smullyan because her dad teaches at Marquette and had Smullyan's book on his shelf. Stacy is the one who would actually solve this if I gave it to her, so I should probably also give it to her.
Mr. Tibbs is a Syrian golden hamster Mrs. Helquist got from the Petland in Brookfield in August. He lives in the back-corner cage near the reading rug. He can squeak yes-and-no to questions if Mrs. Helquist holds up a sunflower seed but mostly he just runs on his wheel. I included him as the third speaker because the puzzle needed three and also because Mrs. Helquist will laugh when she sees it on Monday.
back of the sheet — working solution
try Eric = TRUTH → Stacy fibs → "Tibbs and I not both truth" is false → both ARE truth-tellers → but Stacy is a fibber. NO.
try Stacy = FIBBER → her stmt is false → both ARE truth-tellers → but she is a fibber. NO.
so: Eric = FIBBER. Stacy = TRUTH-TELLER. Mr. Tibbs = FIBBER. check 3: Tibbs fibs → "Eric is truth" is false → Eric fibs ✓ all three statements consistent. unique solution.
figured it out 8:31pm during dad's W-A-X turn for 28 points — solved before Kendra got back from the bathroom — kendra figured it out too at 8:38pm after I showed her the trick — B.S., 5th grade, Underwood Elem., age 11.
SELCHOW & RIGHTER — SCRABBLE BRAND CROSSWORD GAME