▁and ▁A . G . ▁and ▁M . E . ▁O wen ▁Chair ▁of ▁Mathemat ics ▁at ▁the ▁Texas ▁A & M ▁University . ▁He ▁is ▁known ▁for ▁his ▁contributions ▁to ▁several ▁fields ▁of ▁mathematics , ▁including ▁functional ▁analysis , ▁probability ▁theory , ▁harm onic ▁analysis , ▁and ▁operator ▁theory . ▁He ▁has ▁also ▁made ▁fundamental ▁contributions ▁to ▁the ▁theory ▁of ▁ ▁C * - al gebras . ▁G illes ▁is ▁the ▁younger ▁brother ▁of ▁French ▁actress ▁Marie - France ▁P is ier . ▁ ▁Research ▁P is ier ▁has ▁obtained ▁many ▁fundamental ▁results ▁in ▁various ▁parts ▁of ▁mathematical ▁analysis . ▁ ▁Ge ometry ▁of ▁Ban ach ▁spaces ▁ ▁In ▁the ▁" local ▁theory ▁of ▁Ban ach ▁spaces ", ▁P is ier ▁and ▁Bernard ▁Ma ure y ▁developed ▁the ▁theory ▁of ▁R adem acher ▁type , ▁following ▁its ▁use ▁in ▁probability ▁theory ▁by ▁J . ▁Hoff man – J org ensen ▁and ▁in ▁the ▁character ization ▁of ▁Hil bert ▁spaces ▁among ▁Ban ach ▁spaces ▁by ▁S .   K w ap ie ń . ▁Using ▁probability ▁in ▁vector ▁spaces , ▁P is ier ▁proved ▁that ▁super - ref lex ive ▁Ban ach ▁spaces ▁can ▁be ▁ren orm ed ▁with ▁the ▁mod ulus ▁of ▁uniform ▁convex ity ▁having ▁" power ▁type ". ▁His ▁work ▁( with ▁Per ▁En f lo ▁and ▁J or am ▁L inden stra uss ) ▁on ▁the ▁" three – space ▁problem " ▁influenced ▁the ▁work ▁on ▁quasi – norm ed ▁spaces ▁by ▁N ig el ▁Kal ton . ▁