“We can only see a short distance ahead, but we can see plenty there that needs to be done.”

Alan Turing (23 June 1912 – 7 June 1954)

APRIL 24 2021 — To celebrate Alan Turing featuring on the new £50 banknote, GCHQ has created their hardest puzzle ever in his honour. Follow us on Twitter: @INTEL_TODAY

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So far, we have worked out the solutions of the first four puzzles. Let us take a look at the 5th puzzle of this magnificent challenge!

Puzzle #5 — Foil

Alan Turing provided the theoretical underpinnings for the modern computer. The image of the microchip on the foil is a recognition of that achievement.

Complete the two sunflowers with four letter words spelt outwards from the central 50s, so that adjacent words differ by exactly one letter.

The example on the left shows how BANK can be changed to NOTE in four steps.

Once you have completed the sunflowers, find the central four letter word which differs by exactly one letter from each of the two words it’s connected to through the microchips, to solve the puzzle!

This puzzle is not particularly difficult and all crossword puzzles aficionados will easily solve it.

Therefore, I would rather take this opportunity to tell you something that is quite remarkable and completely counter-intuitive.

First, you do not have to solve the top flower to find the answer of that part.

Second, you do not even need to find the answer of the bottom flower to solve this puzzle.

I can hear you thinking: “This cannot possibly be true!”

Surely, you must think that I am kidding?

The answer to the top flower

Did you notice (at about 9 o’clock) the sequence: * W U * ?

There is only ONE word in English: S W U M !

[You can use this WordFinder tool if you are not sure!]

And now, consider the next three sequences, rotating anti-clockwise.

Line 1 S W U M
Line 2 * * * *
Line 3 G * * *
Line 4 * * * E

Question — Although we have ZERO information about Line 2, it is clear that the first letter is S! Why?

Since there is only one word such WU, either the W or the U must be replaced from Line 1 to Line 2.

Thus, line 2 looks like this:

Line 1 S W U M
Line 2 S * * M
Line 3 G * * *
Line 4 * * * E

Now, from L2 to L3, S changed into a G, thus the other 3 letters are the same as on the Line above. [I use the = symbol for such cases.]

Line 1 S W U M
Line 2 S * * M
Line 3 G = = M
Line 4 * * * E

By the same method, we can conclude the following about line 4.

Line 1 S W U M
Line 2 S * * M
Line 3 G = = M
Line 4 G = = E

And the next line starts with a B and the following (The answer) ends with a B.

Line 1 S W U M
Line 2 S * * M
Line 3 G = = M
Line 4 G = = E
Line 5 B = = E
Line 6 B = = B

This is GOLD! The letters in position 2 and 3 are the same from Line 2 to Line 5!

So, do we keep the W or the U?

That is easy to answer as there are no 4 Letter word (see line 3) starting with GW and Ending in M. Thus the 3rd letter is U!!!

Line 1 S W U M
Line 2 S * U M
Line 3 G = U M
Line 4 G = U E
Line 5 B = U E
Line 6 B = U B

And there is only ONE 4 letter word that starts with B and ends with UB.

Thus, the answer of top wheel is BLUB.

Please, notice that we did not work out the puzzle at all. W just found the solution.

I think that Turing would have loved this way of getting the answer.

Now that I have proved my first statement, let us go back to the second one.

“It is not necessary to find the answer of the bottom wheel to solve the puzzle.”

What do you think? Am I joking? Or is it true?

See you next week…

REFERENCES

Alan Turing — a short biography by Andrew Hodges

The Turing Challenge — GCHQ

GCHQ releases ‘most difficult puzzle ever’ in honour of Alan Turing — The Guardian

The list of all words in the top flower are:

SWUM
SWAM
SWAP
SOAP
SLAP
SLIP
SLID
SAID
SAND
SEND
SEED
SPED
SPUD
SPUR
SLUR
BLUR
BLUB
BLUE
GLUE
GLUM
SLUM
SWUM

=

GCHQ — Play the TURING Challenge! [How to get the Answer to Puzzle #5… Without solving Puzzle #5]