Written with feet upside down (7)

I believe the answer is:

inverse

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

I cannot understand how the remainder of the clue works.

(Other definitions for inverse that I've seen before include "Opposite in direction" , "Reversed in order or relation" , "Upside down - opposite in effect" , "Transposed" , "Antonym" .)

I've seen this clue in The Independent.

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