After consideration? No? (2,10)

I believe the answer is:

on reflection

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

'no?' is the definition.
Both the definition and answer are singular nouns.
Perhaps there's a link between them I don't understand?

'after consideration?' is the wordplay.
'after' becomes 'on' (I can't justify this - if you can you should give a lot more credence to this answer).
'consideration?' becomes 'reflection' (both can mean thinking about something).
'on'+'reflection'='ON REFLECTION'

Can you help me to learn more?

I've seen this clue in the Sydney Morning Herald.

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