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When all is fair (2,4,3,3)

Ross

I believe the answer is:

in love and war

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

'when' is the definition.
I don't know anything about this answer so I can't tell whether it can be defined by this definition.

'all is fair' is the wordplay.
I cannot really understand how this works, but
'all' could be 'love' (I've seen this before) and 'love' is present in the answer.
This explanation may well be incorrect...

Can you help me to learn more?

I've seen this clue in The Irish News.
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