A useful person to study diplomacy (7)

I believe the answer is:

contact

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'a useful person' is the definition.
'contact' can be an answer for 'person' (contact is a kind of person). I'm not sure about the 'a useful' bit.

'study diplomacy' is the wordplay.
'study' becomes 'con' (con can mean to study).
'diplomacy' becomes 'tact' (tact can mean diplomacy or sensitivity).
'con'+'tact'='CONTACT'

'to' is the link.

Can you help me to learn more?

(Other definitions for contact that I've seen before include "Useful acquaintance" , "Meeting" , "Communication" , "Juxtaposition" , "Connection" .)

I've seen this clue in The Irish News.

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