Wealthy types act fast to become corrupt (3,4)

I believe the answer is:

fat cats

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'wealthy types' is the definition.
The definition suggests a plural noun which matches the answer.

'act fast to become corrupt' is the wordplay.
'act fast' can be anagrammed to 'FAT CATS'.
But, I'm not clear how the anagram is indicated.

Can you help me to learn more?

(Other definitions for fat cats that I've seen before include "Leaders of commerce" , "important people" , "wealthy businessmen produced" , "Large Persians" .)

I've seen this clue in The Independent.

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