<s>
In	O
computer	B-General_Concept
science	I-General_Concept
,	O
well-founded	B-Application
semantics	I-Application
is	O
a	O
semantics	B-Application
for	O
logic	B-Language
programming	I-Language
.	O
</s>
<s>
In	O
logic	B-Language
programming	I-Language
,	O
a	O
computer	O
receives	O
a	O
set	O
of	O
facts	O
,	O
and	O
a	O
set	O
of	O
"	O
inference	O
rules	O
"	O
about	O
how	O
these	O
facts	O
relate	O
.	O
</s>
<s>
Well-founded	B-Application
semantics	I-Application
is	O
one	O
way	O
to	O
do	O
so	O
.	O
</s>
<s>
Well-founded	B-Application
semantics	I-Application
was	O
defined	O
by	O
Van	O
Gelder	O
,	O
et	O
al	O
.	O
</s>
<s>
The	O
well-founded	B-Application
semantics	I-Application
can	O
be	O
viewed	O
as	O
a	O
three-valued	B-Language
version	O
of	O
stable	B-Application
model	I-Application
semantics	I-Application
.	O
</s>
<s>
but	O
whether	O
specimen	O
A	O
flies	O
during	O
the	O
day	O
is	O
unknown	O
,	O
well-founded	B-Application
semantics	I-Application
would	O
assign	O
the	O
proposition	O
``specimen	O
A	O
is	O
a	O
moth``	O
the	O
value	O
bottom	O
which	O
is	O
neither	O
true	O
nor	O
false	O
.	O
</s>
<s>
Well-founded	B-Application
semantics	I-Application
is	O
a	O
way	O
of	O
making	O
safe	O
inferences	O
in	O
the	O
presence	O
of	O
contradictory	O
data	O
such	O
as	O
noisy	O
data	O
,	O
or	O
data	O
acquired	O
from	O
experts	O
who	O
promote	O
varying	O
opinions	O
.	O
</s>
<s>
Many	O
two-valued	O
semantics	B-Application
do	O
not	O
consider	O
such	O
a	O
problem	O
state	O
workable	O
.	O
</s>
<s>
Well-founded	B-Application
semantics	I-Application
,	O
however	O
,	O
circumvents	O
the	O
contradictions	O
and	O
proceeds	O
to	O
derive	O
as	O
many	O
two-valued	O
facts	O
as	O
possible	O
,	O
even	O
though	O
some	O
consequences	O
may	O
remain	O
unknown	O
.	O
</s>
<s>
The	O
fastest	O
known	O
algorithm	O
to	O
compute	O
well-founded	B-Application
semantics	I-Application
,	O
is	O
of	O
quadratic	O
complexity	O
.	O
</s>
