A little mathematical challenge, it's said (4)

I believe the answer is:

some

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'a little' is the definition.
(I've seen this before)

I don't understand the remainder of the clue.

(Other definitions for some that I've seen before include "Several" , "A little; not a little" , "Undefined number" , "An undetermined number" , "Part" .)

I've seen this clue in The Telegraph.

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