Six Signatures. One Of Them Is Impossible. Can You Find It?
A new puzzle for the back of the book. You are given six custody entries for a single folder and the movements of the six people who signed them. Exactly one entry cannot have happened. Find it.
A third puzzle joins the acrostic and the cryptogram, and it is the one this newspaper should probably have run first, because it is the thing the documents desk does all day.
A custody chain is a list of who held a folder, where, and when. A forged chain almost never fails on the signatures. It fails on the geography — somebody is recorded receiving a folder in a place they could not have been.
Below is a chain of six entries. Below that, what we know about where each signatory was. Exactly one entry is impossible. The other five are consistent.
You do not need any outside knowledge. Everything required is on this page.
The chain
| # | Date | Received by | At | Signed |
|---|---|---|---|---|
| 1 | 3 Mar | R. Okonjo-Halstead | Perth registry | 09:40 |
| 2 | 7 Mar | T. Bergkamp-Rios | Perth registry | 16:05 |
| 3 | 11 Mar | A. Delacroix-Whitby | Singapore annex | 11:20 |
| 4 | 14 Mar | W. Oyelaran-Tasker | Singapore annex | 08:15 |
| 5 | 19 Mar | C. Adeyemi-Strand | Zurich store | 14:50 |
| 6 | 22 Mar | H. Oyelowo-Vasquez | Zurich store | 10:30 |
What we know about the six
- Okonjo-Halstead was in Perth for the whole of March. He signs for a great many things and has never been anywhere interesting.
- Bergkamp-Rios flew Perth to Singapore on the evening of 7 March and did not return.
- Delacroix-Whitby was in Singapore from 9 March to 16 March, then Zurich from 18 March.
- Oyelaran-Tasker was in Zurich until the morning of 14 March, and in Singapore from the 15th.
- Adeyemi-Strand was in Zurich for the whole of March.
- Oyelowo-Vasquez was in Singapore until 20 March, then Zurich from the 21st.
The rule
A folder cannot be received by someone who was not in that city on that date. It also cannot be received in a city it has not yet travelled to — the chain runs in order, and a folder in Zurich on the 19th cannot be back in Singapore on the 22nd.
The answer
Entry 4. Oyelaran-Tasker was in Zurich on the morning of 14 March and did not reach Singapore until the 15th. She cannot have signed in the Singapore annex at 08:15 on the 14th.
Every other entry survives. Bergkamp-Rios signs in Perth at 16:05 on the 7th and flies that evening, which is tight but legal. Delacroix-Whitby is in Singapore on the 11th and Zurich from the 18th, so entry 3 holds and she is not needed again. Oyelowo-Vasquez reaches Zurich on the 21st and signs on the 22nd, with a day to spare.
The reason this puzzle is worth setting is that entry 4 is the only one that looks completely ordinary. It has a plausible name, a plausible time and the same city as the entry above it. The impossible entry in a real forged chain is almost never the strange one. It is the one that matches its neighbour.
Custody Chain No. 2 runs next week and has seven entries and two impossibilities. One of them is in the times.
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Corrections to this story
- clarification — The puzzle asked readers to find the one entry in a custody chain that could not have happened, and the intended answer, entry 4, stands. A reader established that entry 2 was also arguable: it has a signatory signing in the Perth registry at 16:05 and flying to Singapore the same evening, which is legal only if the registry, the drive and the check-in all cooperate. The puzzle never said where the Perth registry was. A solver could not settle the question from the page.How it happened: The chain gave every signatory's itinerary and none of the registries' addresses. A puzzle whose answer turns on whether a journey is possible has to say where the journeys start and end; this one assumed it and did not print it. The setter checked the geography and did not check the clock.What we changed: Every registry in this series now carries its address and its distance from the nearest airport. Custody Chain No. 2, published today, is built on that rule — one of its two impossibilities cannot be seen without it, and nobody in that entry is in the wrong place.
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