Determined those people will accept alternative work on collections? (3,6)

I believe the answer is:

set theory

I'm a little stuck... Click here to teach me more about this clue!

'work on collections?' is the definition.
The definition and answer can be both related to thinking as well as being singular nouns.
Maybe you can see a link between them that I can't see?

'determined those people will accept alternative' is the wordplay.
'determined' becomes 'set' (synonyms).
'those people' becomes 'they' ('they' refers to a group of people).
'will accept' indicates putting letters inside.
'alternative' becomes 'or'.
'they' placed around 'or' is 'theory'.
'set'+'theory'='SET THEORY'

Can you help me to learn more?

(Another definition for set theory that I've seen is " Cantor started this".)

I've seen this clue in The Guardian.

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