Mathematician touring Hanoi finally, a capital city (6)

I believe the answer is:

vienna

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'capital city' is the definition.
(capital of Austria)

'mathematician touring hanoi finally a' is the wordplay.
'mathematician' becomes 'venn' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'touring' is an insertion indicator (tour can mean to go around).
'finally' indicates one should take the final letters.
The last letter of 'hanoi' is 'i'.
'venn' enclosing 'i' is 'vienn'.
'vienn'+'a'='VIENNA'

Can you help me to learn more?

(Other definitions for vienna that I've seen before include "Capital city of Austria" , "Austria's capital city" , "somewhere in Austria" , "European capital" , "huge 20 [ULTRAVOX] hit" .)

I've seen this clue in The Guardian.

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