Maud's not all there! Here! (5)

I believe the answer is:

adsum

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

'maud's not all there' is the wordplay.
'maud's' can be anagrammed to 'ADSUM'.
But, I'm not clear how the anagram is indicated.

Can you help me to learn more?

(Another definition for adsum that I've seen is " here".)

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

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