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Remark: ‎‎The ‎idea ‎of ‎this soft ‎question ‎is ‎adopted ‎from ‎the following interesting ‎book‎. ‎ ‎

Timothy Gowers, Mathematics: A Very Short Introduction, Oxford University Press, 2002.‎ ‎

$‎‎40$ ‎years ‎old ‎is a‎ ‎well ‎known ‎bound ‎for professional ‎mathematicians. ‎Many ‎of ‎them ‎believe ‎that ‎this ‎age ‎is ‎an ‎end ‎for a‎ ‎mathematician's masterworks. ‎Based on ‎the ‎soul ‎of ‎this ‎belief ‎many ‎of ‎the ‎most ‎famous ‎mathematical ‎awards (like fields medal) ‎are ‎just ‎for ‎mathemticians ‎who ‎are under ‎‎$40‎‎$ ‎years ‎old. ‎Now ‎my ‎question ‎is:‎ ‎

Question: Do you know any mathematician who proved his/her best theorems after ‎$‎‎40$ ‎years ‎old? ‎Please ‎introduce ‎your ‎references.‎ ‎ ‎

Remark: ‎The ‎notion ‎of "‎the ‎masterwork" ‎of ‎a mathematician ‎is ‎clear ‎by ‎the fame and ‎number ‎of ‎references ‎to it.‎ ‎

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