US criminal and others embracing universal proposal is an impossibility? (9,6)

I believe the answer is:

perpetual motion

I'm a little stuck... Click here to teach me more about this clue!

'an impossibility?' is the definition.
Both the definition and answer are singular nouns.
Perhaps they are linked in a way I don't understand?

'us criminal and others embracing universal proposal' is the wordplay.
'us criminal' becomes 'perp' (US slang for perpetrator).
'and others' becomes 'etal' (short for 'et alia', 'and others' in Latin).
'embracing' indicates putting letters inside.
'universal' becomes 'U' (film certificate).
'proposal' becomes 'motion' (proposal at a meeting).
'etal' enclosing 'u' is 'etual'.
'perp'+'etual'+'motion'='PERPETUAL MOTION'

'is' acts as a link.

Can you help me to learn more?

(Other definitions for perpetual motion that I've seen before include "Always going" , "that keeps on going" .)

I've seen this clue in The Times.

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