Crossword Genius

Prove a race isn't fixed (9)

Ross

I believe the answer is:

ascertain

'prove' is the definition.
(thesaurus)

'a race isn't fixed' is the wordplay.
'fixed' indicates an anagram.
'race'+'isnt'='raceisnt'
'raceisnt' with letters rearranged gives 'scertain'.
'a'+'scertain'='ASCERTAIN'

(Other definitions for ascertain that I've seen before include "Find out for sure, determine" , "Prove" , "Find out - make sure" , "settle" , "Verify" .)

I've seen this clue in The Telegraph.
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