Crossword Genius

At that point? Working on that (7)

Ross

I believe the answer is:

thereon

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'on that' is the definition.
(synonyms)

'at that point? working' is the wordplay.
'at' means one lot of letters go next to another.
'that point?' becomes 'there' (I can't justify this - if you can you should give a lot more credence to this answer).
'working' becomes 'on' (on can mean working or activated).
'there'+'on' is 'THEREON'.

Can you help me to learn more?

(Other definitions for thereon that I've seen before include "Following from the thing just mentioned" , "At that point" .)

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