Understanding exercise function requires no energy (10)

I believe the answer is:

perception

'understanding' is the definition.
(thesaurus)

'exercise function requires no energy' is the wordplay.
'exercise' becomes 'pe' (Physical Education).
'function' becomes 'reception ' (type of event or function).
'requires no' suggests deleting specific letters.
'energy' becomes 'e' (physics symbol as in E=mc2).
'reception' with 'e' taken out is 'rception'.
'pe'+'rception'='PERCEPTION'

(Another definition for perception that I've seen is " View".)

I've seen this clue in The Guardian.

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