Denomination one in argument against procedure (1-7)

I believe the answer is:

c-section

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'procedure' is the definition.
The definition and answer can be both acts as well as being singular nouns.
Maybe they are linked in a way I don't understand?

'denomination one in argument against' is the wordplay.
'denomination' becomes 'sect' (I've seen this before).
'one' becomes 'I' (Roman numeral).
'in' indicates putting letters inside.
'argument against' becomes 'con' (I've seen this in other clues).
'sect'+'i'='secti'
'secti' placed within 'con' is 'C-SECTION'.

Can you help me to learn more?

I've seen this clue in The Independent.

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