Omit to indicate permission is not possible (8)

I believe the answer is:

leaveout

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'omit to indicate' is the definition.
I know nothing about this answer so I can't judge whether this works.

'permission is not possible' is the wordplay.
'permission' becomes 'leave' (leave is permission or authorisation).
'is not possible' becomes 'out' (I can't justify this - if you can you should believe this answer much more).
'leave'+'out'='LEAVEOUT'

Can you help me to learn more?

I've seen this clue in The Irish Independent.

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