ermann ▁function ▁( 1 9 2 8 ). ▁ ▁Gabriel ▁Sud an ▁received ▁his ▁Ph . D . ▁from ▁the ▁University ▁of ▁Gött ingen ▁in ▁ 1 9 2 5 ▁for ▁his ▁th esis ▁Über ▁die ▁ge ordnet en ▁M engen ▁(" On ▁the ▁theory ▁of ▁ordered ▁sets "), ▁super vised ▁by ▁David ▁Hil bert . ▁ ▁He ▁taught ▁at ▁the ▁Poly techn ic ▁University ▁of ▁Buch ar est ▁from ▁ 1 9 4 1 ▁until ▁his ▁ret irement , ▁in ▁ 1 9 6 6 . ▁▁ ▁Sud an ▁constructed ▁the ▁function ▁that ▁be ars ▁his ▁name ▁with ▁the ▁same ▁aim ▁as ▁Wilhelm ▁A ck ermann : ▁to ▁solve ▁in ▁the ▁aff irm ative ▁a ▁problem ▁raised ▁by ▁Hil bert . ▁The ▁A ck ermann ▁and ▁Sud an ▁functions ▁ ▁are ▁chron olog ically ▁the ▁first ▁examples ▁of ▁recursive ▁functions ▁which ▁are ▁not ▁primitive ▁recursive . ▁ ▁References ▁ ▁Crist ian ▁Cal ude , ▁Sol omon ▁Marcus , ▁I onel ▁Te vy , ▁The ▁first ▁example ▁of ▁a ▁recursive ▁function ▁which ▁is ▁not ▁primitive ▁recursive , ▁Historia ▁Mathemat ica ▁ 6 ▁( 1 9 7 9 ), ▁no . ▁ 4 , ▁ 3 8 0 – 3 8 4 ▁▁ ▁Sol omon ▁Marcus , ▁" Gr ig ore ▁C . ▁Mo is il : ▁A ▁life ▁becoming ▁a ▁myth ", ▁International ▁Journal ▁of ▁Comput ers , ▁Communic ations ▁& ▁Control , ▁vol . ▁ 1 ▁( 2 0 0 6 ), ▁no . ▁ 1 , ▁ 7 3 – 7