<s>
In	O
backtracking	B-Algorithm
algorithms	I-Algorithm
,	O
look	O
ahead	O
is	O
the	O
generic	O
term	O
for	O
a	O
subprocedure	O
that	O
attempts	O
to	O
foresee	O
the	O
effects	O
of	O
choosing	O
a	O
branching	B-General_Concept
variable	O
to	O
evaluate	O
one	O
of	O
its	O
values	O
.	O
</s>
<s>
The	O
two	O
main	O
aims	O
of	O
look-ahead	B-Application
are	O
to	O
choose	O
a	O
variable	O
to	O
evaluate	O
next	O
and	O
the	O
order	O
of	O
values	O
to	O
assign	O
to	O
it	O
.	O
</s>
<s>
In	O
a	O
general	O
constraint	B-Application
satisfaction	I-Application
problem	I-Application
,	O
every	O
variable	O
can	O
take	O
a	O
value	O
in	O
a	O
domain	O
.	O
</s>
<s>
A	O
backtracking	B-Algorithm
algorithm	I-Algorithm
therefore	O
iteratively	O
chooses	O
a	O
variable	O
and	O
tests	O
each	O
of	O
its	O
possible	O
values	O
;	O
for	O
each	O
value	O
the	O
algorithm	O
is	O
recursively	O
run	O
.	O
</s>
<s>
A	O
look-ahead	B-Application
technique	O
that	O
may	O
be	O
more	O
time-consuming	O
but	O
may	O
produce	O
better	O
results	O
is	O
based	O
on	O
arc	O
consistency	O
.	O
</s>
<s>
The	O
most	O
common	O
way	O
of	O
using	O
look-ahead	B-Application
for	O
solving	O
constraint	B-Application
satisfaction	I-Application
problems	I-Application
is	O
the	O
maintaining	O
arc-consistency	O
(	O
MAC	O
)	O
algorithm	O
.	O
</s>
<s>
In	O
particular	O
,	O
for	O
any	O
unassigned	O
variable	O
and	O
value	O
,	O
look-ahead	B-Application
estimates	O
the	O
effects	O
of	O
setting	O
that	O
variable	O
to	O
that	O
value	O
.	O
</s>
