thiet mot phan phep ghep nhu sau:
M o 0 1 0 0 tl 2 1 0 0
N h u vay, sau hinh t h M dau tien da c6, nh5 nhung domino drfÓ' thu nap bdi cac bo phan 2 - 4, ta kiSn thigt them hinh thai t h i l hai-
1.4 Mot vai bdi todn khong gidi duac 109
Ta mong sao qua t r i n h nay duqc tigp di6n, tutc them hinh thai thiJ ba, hinh thai thuf t u va cac hinh thai tigp theọ Dg dieu n^y dign ra, ta phai thgm nhieu domino vdi su lap lai cua ky ttr tJ.
B o p h a n 5.
Dua va [ ^ 1
.011. vao P'.
C) day domino thu: nhat duoc sut dung dg ngSn each cae hinh thai vdi nhau; domino t h i i hai giup ta ket thuc mo ta hinh thai ca
biet uq0 khi ma dau doc-ghi vUdt qua dau phai eiia u, la ttr bigu
di§n noi dung trgn bang.
Tiep tuc vdi t h i du neu trgn, gia sii khi d trang thai qi va doc ky t u 1 tren bang, may M chuygn sang trang thai qs, thay ky
t i l 1 bang 0 va di chuygn dau doc-ghi sang bgn phai; nghia la,
6{qi, 1) = (^2,0, R.)- K h i do bo phan 2 t h u nap vao P' domino
.0 92. '
Nhd domino n^y, phep ghep tigp tuc duqc kien thiet n h u sau:
'Sy gi5, gia sii v^o mot thdi d i l m nao do, khi 6 hinh thai 2 O 9 3 O I
% M chuygn true tiep sang hinh thai 2 ^4011, bdi phep bign d5i
W ban 6{q3, 0) = ( 5 4 ,1 , L). Theo bo phan 3, trong P' c6 cac domino
. 9 4 O I . "lc/30" "lc/30" 9 4 I I . 2^30" .9421. va " 0 9 3 O " . 9 4 0 1 .
110 May Turing va Thuat toan
Domino dku tien d day la hop ly bdi vi ky t u ben trai dau doc-ghi
la 0. Domino k i i u cuoi ciing chi duoc sii dung dg mo ta hinh thai
dang ca biet q0u khi dau doc ghi vuat qua dau trai cua u, la t i i
bigu dign noi dung trgn bang. K h i do, lua chon thich hop nhiing
domino c6 trong P', ta tiep tuc kien thiet phep ghep nhu sau:
Trcl lai viec chiing minh. Vdi nhiJng domino dUdc thu nap vao P'
den th5i digm nay, ta de dang kien thigt phep ghep diem ta qua
trinh tinh toan cua may Turing Af trgn dau vao w. Cu t h l hon,
ta CO thg chia viec kien thiet thanh tiing cong doan. Cong doan dau tien s^p dat mieng ghep thii nhat vdi dong dirdi dien ta hinh
thai ban dau cua Af. M5i cong doan tiep theo bao gom viec lua chpn ill P' cac domino thich hop roi s^p xep chung lien nhau sao
cho dong trgn va dong dudi tudng ling vdi hai hinh thai ke tiep
nhau trong qua trinh tinh toan cua Af trgn w. Nhu vay, sau moi
cong doan, dong tren v^ dorlg dudi cua phep ghep deu dign ta qua trinh chuyin doi hinh thai cua A/, nhung d6ng tren "dien ta cham hon" mot hinh thaị Viec kign thiet nay se tiep dign mai mai, neu
qua trinh tinh toan cua Af trgp w khong đng. Nguoc lai, neu Af d t o g trgn w t h i sau mot cong doan kien thiet n^o đ, 6 cuoi dong
dudi cua phep ghep xuat hien hinh thai ditng cua M , chang han
nhu uq^u vdi = q^ ho&c q^ = q^. Do viec "dign ta cham hon"
cua dong trgn, ngn trong trildng hop nay dg cd thg kien thiet dildc phep ghep thanh cong, ta mong sao phan cuoi dong trgn cua phep ghep "dudi kip" dong dudị Dg dat duoc mong mu6n nhu vSy, ta
dua them vho P' nhiing domino vdi dSc tinh "thu don" hiiu ich.
1.4 Mot vai bai toan khong gidi dtcac 111
B 6 phan 6. D6i vdi m6i a G T , dua vko P' hai loai domino sau:
'ạq^' 'q^Sí
va