Foremost of maestri so up and down with movement (5)

I believe the answer is:

mosso

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'foremost of maestri so up and down with movement' is the definition.
I can't judge whether this definition defines the answer.

'foremost of maestri so up and down with' is the wordplay.
'foremost of' says to take the initial letters.
'up' says the letters should be written backwards (in down clue: letters go upwards).
'and' is a charade indicator (letters next to each other).
'down with' becomes 'so' (I can't explain this - if you can you should believe this answer much more).
The first letter of 'maestri' is 'm'.
'so' in reverse letter order is 'os'.
'm'+'os'+'so'='MOSSO'

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I've seen this clue in The Independent.

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