Checks for "F” in nymphs (10)

I believe the answer is:

proofreads

'checks' is the definition.
(proofreading is a kind of checking)

'for f in nymphs' is the wordplay.
'for' becomes 'pro' (as in being 'pro' something).
'in' means one lot of letters goes inside another.
'nymphs' becomes 'oreads' (I've seen this in another clue).
'f' inserted into 'oreads' is 'ofreads'.
'pro'+'ofreads'='PROOFREADS'

(Another definition for proofreads that I've seen is " checks for some answers here - with 23d".)

I've seen this clue in The Times and The Sunday Times.

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