Crossword Genius

Gave the impression, when one happened on (4,6)

Ross

I believe the answer is:

came across

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'gave the impression' is the definition.
The answer and definition can be both related to thinking as well as being past participle verbs.
Perhaps there's a link between them I don't understand?

'one happened on' is the wordplay.
'one' becomes 'across' (I can't justify this - if you can you should believe this answer much more).
'happened' becomes 'came' (coming is a kind of happening).
'on' says to put letters next to each other.
'across' put after 'came' is 'CAME ACROSS'.

'when' acts as a link.

Can you help me to learn more?

(Another definition for came across that I've seen is " Found".)

I've seen this clue in the Evening Standard.
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