Hair treatment to interest the pools fan (4)

I believe the answer is:

perm

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'hair treatment' is the definition.
(I've seen this in another clue)

I don't understand how the rest of the clue works.

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(Other definitions for perm that I've seen before include "Possibility in pool" , "A hairdo; Urals city" , "Russian city and hairstyle, in short" , "Hair setting treatment; pools selection system" , "Hair style (abbr)" .)

I've seen this clue in the Evening Standard.

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