From Newsgroup: comp.lang.prolog

after 2 months fixed the prolog bug

DATA.txt

bro tom brad <-------------- try 1
friend brad fredy
bro tom bill <----------------try 2
friend bill fry
friend fry fryfry
rich gaga
pretty gaga
old gaga
daughter brad shelly
friend dob ellen <--------answer
daughter bill dob


PROGRAMS.txt

niece P NIECE
bro P BRO
daughter BRO NIECE

fon P F
niece P N
friend N F




you ask FRIENDOFNIECE tom X ?

and it finds 2 nieces until it finds a friend of one... after the ORANGE BOX it backtracks to re-run NIECE P N
it tries tom's other brother







fon tom X
fon P F

tom >> P
X << F
X >> F
P===tom
F===X

FIND : fon . tom . X .

TAILNUM 2-1 niece P N
P=<=tom
TAILQUERY: niece..tom..N


TAILFIND : niece . tom . N .
niece tom N
niece P NIECE

NIECE ::= N
N ::== NIECE

TAILNUM 1-1 bro P BRO
P=<=tom
TAILQUERY: bro..tom..BRO


TAILFIND : bro . tom . BRO .
bro tom BRO
bro tom brad

P ::== tom
BRO ::== brad

TAILNUM 1-2 daughter BRO NIECE
BRO=<=brad
TAILQUERY: daughter..brad..NIECE


TAILFIND : daughter . brad . NIECE .
daughter brad NIECE
daughter brad shelly

BRO ::== brad
NIECE ::== shelly
CALLTAIL:0
CALLTAIL:2

TAILNUM 2-2 friend N F
N=<=shelly
TAILQUERY: friend..shelly..F


TAILFIND : friend . shelly . F .
friend shelly F

ANS -1
2-2 friend N F
P=<=tom
TAILQUERY: bro..tom..BRO


TAILFIND : bro . tom . BRO .
bro tom BRO
bro tom bill

P ::== tom
BRO ::== bill

TAILNUM 1-2 daughter BRO NIECE
BRO=<=bill
TAILQUERY: daughter..bill..NIECE


TAILFIND : daughter . bill . NIECE .
daughter bill NIECE
daughter bill dob

BRO ::== bill
NIECE ::== dob
CALLTAIL:0
CALLTAIL:2

TAILNUM 2-2 friend N F
N=<=dob
TAILQUERY: friend..dob..F


TAILFIND : friend . dob . F .
friend dob F
friend dob ellen

N ::== dob
F ::== ellen
CALLTAIL:0
niece P NIECE



CALLTAIL:0

YES

X = ellen



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