From Newsgroup: comp.lang.prolog
********************* DATA ************************
bro tom brad
friend brad fredy
bro tom bill *
friend bill fry
friend fry fryfry
rich gaga
pretty gaga
daughter brad shelly
friend dob ellen *
daughter bill dob *
******************** PROGRAMS ******************
sibling AA BB
bro AA BB
nees P N
sibling P S
daughter S N
fonees X Y
nees X N
friend N Y
********************* TRACE **********************
ENGINE 0 1 fon tom FFF
fon tom FFF
fon P F
ANS2 2
fon -- fon
tom -- P
FFF -- F
ENGINE 2 1 niece P N
niece P N
niece P NIECE
ANS2 1
niece -- niece
P -- P
N -- NIECE
ENGINE 1 1 bro P BRO
bro P BRO
bro guy brotha
ANS2 12
d*1*1---
ENGINE 1 2 daughter BRO NIECE
daughter BRO NIECE
daughter bill dob
ANS2 23
d*1*1---d*1*2---
ENGINE 2 2 friend N F
friend N F
friend brad fredy
ANS2 15
d*1*1---d*1*2---d*2*2---
STACK3UPTO1
HERE0
P = tom
bro tom BRO
bro tom brad
BRO << brad
UPTO2
HERE0
BRO = brad
NIECE = N
daughter brad N
daughter brad dooby
N << dooby
UPTO3
HERE0
N = dooby
F = FFF
friend dooby FFF
UPTO2
HERE0
NIECE = N
daughter BRO N
daughter bill dob
BRO << bill
N << dob
UPTO3
HERE0
N = dob
F = FFF
friend dob FFF
friend dob ellen
FFF << ellen
YES
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