M CO diTng hay khong tren w la yeu to quyet dinh su ton tai thuat
2. Neu H chap nhan, bac bo va neu H bac bo, chap nhan"
Khong nen boi roi vdi y tudng cho may thiTc hien t i n h toan tren t i t
bigu dien chinh no bdi v i , vg nguyen tac, may Turing c6 thg duoc ma hoa b^ng mot t i t tren chinh bang chu: cua maỵ M a t khac, trong thitc tg, digu do tuong t u nhit viec cho chay mot chuong t r i n h ma chinh no dUdc coi nhu dau vaọ Noi torn lai,
(accept neu M khong chap nhan (A/), , ~ [reject neu A/ chap nhan ( A f ) .
Dieu gi xay ra khi ta cho mdy C tinh toan trgn dau vao (C), tiic
1.4 Mot vai bai toan khong gidi dicac 95
tren tfit b i l u dign chinh nỏ lYong trudng hop nay ta t h u duQc
C({C)) = h^^^P^ C khong chap nhan (C),
[reject neu C chap nhan ( C ) .
Nhu vay, dua theo may gia dinh H ta dg dang xay dung dxiac mdy Turing C, va trong ket qua tinh toan cua C ro rang c6 dieu phi lỵ Mau t h u l n nay chilng to r^ng may Turing H khong thg ton taị
Dinh ly 1.4.1 dudc chiing minh, tiJc bai toan chap nhan d6i vdi
may Turing la khong giai dudc. •
Ta hay xem lai cac budc chiing m i n h dinh ly naỵ Gia t h i i r^ng
may H khang dinh ngon ngii ATM- K h i do sijf dung H ta xay dung
may Turing C sao cho dau vao (A/) dirqc chap nhan chinh xac khi
M khong chap nhan (A/). Cuoi cung, ta cho C t i n h toan trgn tiT
bigu dign chinh nọ Nhflng may nay c6 cac hhnh vi sau day, trong
do hanh vi sau ciing chfla mau thuan:
* H chap nhan (Af, w) chinh xac khi M chip nhan w. * C bac bo (A/) chinh xac khi M chap nhan ( M ) . * C bac bo (C) chinh xac khi C chap nhan (C).
Vay t h i phflong phap dirctng cheo diroc ap dung 6 ch6 nao trong chflng m i n h D i n h ly 1.4.1? Dieu nay dfloc bieu lo khi ta khao
sat cac bang hanh v i cua nhflng may Turing H va C. Trong cac
bang ay t a liet kg tat ca cac may Turing doc theo dau cac hang, ^^1) A/2,... va tat ca cac bigu dign cua chung ngang theo dau cdc cQt, (A/i), ( A / 2 ) , . . . Viec t r u y nhap tiep theo chi dflOc thirc hien t a i
cac giao digm gifla hang va cot ma t a i giao diem ay may d hhng chap nhan dau vao d cot. Tai giao digm gifla hang va cot t a di^n
o-ccept neu may chap nhan dau vao va dg trong neu may bac bo
hoac khong dflng trgn dau vao aỵ Y tUcing nay dflOc m i n h hoa trong bang sau daỵ