▁ 1 9 3 0 s . ▁ ▁Tennis ▁career ▁C ul ley ▁reached ▁the ▁quarter final s ▁of ▁the ▁U . S . ▁National ▁Championships ▁in ▁ 1 9 3 6 , ▁defe ating ▁No . ▁ 5 ▁seed ▁and ▁ 1 9 3 1 ▁W im ble don ▁champion ▁Sid ney ▁Wood ▁en ▁route . ▁ ▁References ▁ ▁External ▁links ▁ ▁Tennis ▁Archives ▁ ▁Category : American ▁male ▁tennis ▁players ▁Category : Year ▁of ▁birth ▁missing ▁Category : Year ▁of ▁death ▁missing <0x0A> </s> ▁In ▁comput ability ▁theory , ▁a ▁machine ▁that ▁always ▁hal ts , ▁also ▁called ▁a ▁dec ider ▁or ▁a ▁total ▁T uring ▁machine , ▁is ▁a ▁T uring ▁machine ▁that ▁eventually ▁hal ts ▁for ▁every ▁input . ▁ ▁Because ▁it ▁always ▁hal ts , ▁such ▁a ▁machine ▁is ▁able ▁to ▁decide ▁whether ▁a ▁given ▁string ▁is ▁a ▁member ▁of ▁a ▁formal ▁language . ▁ ▁The ▁class ▁of ▁languages ▁which ▁can ▁be ▁decided ▁by ▁such ▁machines ▁is ▁exactly ▁the ▁set ▁of ▁recursive ▁languages . ▁However , ▁the ▁hal ting ▁problem , ▁determ ining ▁whether ▁an ▁arbitrary ▁T uring ▁machine ▁hal ts ▁on ▁a ▁given ▁input , ▁is ▁itself ▁an ▁und ec id able ▁problem . ▁ ▁Function s ▁comput able ▁by ▁total ▁T uring ▁machines ▁▁ ▁In ▁practice , ▁many ▁functions ▁of ▁interest ▁are ▁comput able ▁by ▁machines ▁that ▁always ▁halt . ▁▁ ▁A ▁machine ▁that ▁uses ▁only ▁finite ▁memory ▁on ▁any ▁particular ▁input ▁can ▁be ▁forced ▁to ▁halt ▁for ▁every ▁input ▁by ▁restrict ing ▁its ▁flow ▁control