▁of ▁World ▁Table ▁Tennis ▁Championships ▁medal ists ▁ ▁References ▁ ▁Category : S wed ish ▁male ▁table ▁tennis ▁players ▁Category : 1 9 0 5 ▁birth s ▁Category : 1 9 6 1 ▁death s ▁Category : World ▁Table ▁Tennis ▁Championships ▁medal ists <0x0A> </s> ▁In ▁mathematics ▁and ▁computer ▁science , ▁Z eno ▁machines ▁( ab bre vi ated ▁Z M , ▁and ▁also ▁called ▁acceler ated ▁T uring ▁machine , ▁AT M ) ▁are ▁a ▁hypoth et ical ▁computational ▁model ▁related ▁to ▁T uring ▁machines ▁that ▁allows ▁a ▁count ably ▁infinite ▁number ▁of ▁algorithm ic ▁steps ▁to ▁be ▁performed ▁in ▁finite ▁time . ▁ ▁These ▁machines ▁are ▁ruled ▁out ▁in ▁most ▁models ▁of ▁computation . ▁ ▁More ▁formally , ▁a ▁Z eno ▁machine ▁is ▁a ▁T uring ▁machine ▁that ▁takes ▁ 2 − n ▁units ▁of ▁time ▁to ▁perform ▁its ▁n - th ▁step ; ▁thus , ▁the ▁first ▁step ▁takes ▁ 0 . 5 ▁units ▁of ▁time , ▁the ▁second ▁takes ▁ 0 . 2 5 , ▁the ▁third ▁ 0 . 1 2 5 ▁and ▁so ▁on , ▁so ▁that ▁after ▁one ▁unit ▁of ▁time , ▁a ▁count ably ▁infinite ▁( i . e . ▁ <0xE2> <0x84> <0xB5> 0 ) ▁number ▁of ▁steps ▁will ▁have ▁been ▁performed . ▁ ▁The ▁idea ▁of ▁Z eno ▁machines ▁was ▁first ▁discussed ▁by ▁Hermann ▁W ey l ▁in ▁ 1 9 2 7 ; ▁the ▁name ▁refers ▁to ▁Z eno ' s ▁par ado xes , ▁attributed ▁to ▁the ▁ancient ▁Greek ▁phil os