 He was fond of saying that math ­ e ­ mat ­ ic ­ al proofs " really aren 't there to convince you that something is true — ​ ​ they 're there to show you why it is true . " The Notices of the American Mathematical Society called him " one of the quiet giants of twentieth @-@ century mathematics , the consummate professor dedicated to scholarship , teaching , and service in equal measure . " 
