Crossword Genius

Number forced into a restricted place, like a triangle (5-8)

Ross

I believe the answer is:

three-cornered

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'a restricted place like a triangle' is the definition.
I can't tell whether this definition defines the answer.

'number forced' is the wordplay.
'number' becomes 'three' (three is a number).
'forced' becomes 'cornered' (I am not sure about this - if you are sure you should believe this answer much more).
'three'+'cornered'='THREE-CORNERED'

'into' acts as a link.

Can you help me to learn more?

I've seen this clue in The Daily Express.
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