<s>
The	O
cut	O
,	O
in	O
Prolog	B-Language
,	O
is	O
a	O
goal	O
,	O
written	O
as	O
!,	O
which	O
always	O
succeeds	O
,	O
but	O
cannot	O
be	O
backtracked	O
.	O
</s>
<s>
Cuts	O
can	O
be	O
used	O
to	O
prevent	O
unwanted	O
backtracking	B-Algorithm
,	O
which	O
could	O
add	O
unwanted	O
solutions	O
and/or	O
space/time	O
overhead	O
to	O
a	O
query	O
.	O
</s>
<s>
Some	O
programmers	O
call	O
the	O
cut	O
a	O
controversial	O
control	O
facility	O
because	O
it	O
was	O
added	O
for	O
efficiency	O
reasons	O
only	O
and	O
is	O
not	O
a	O
Horn	B-Application
clause	I-Application
.	O
</s>
<s>
The	O
use	O
of	O
a	O
cut	O
which	O
only	O
improves	O
efficiency	O
is	O
referred	O
to	O
as	O
a	O
green	B-Application
cut	I-Application
.	O
</s>
<s>
Green	B-Application
cuts	I-Application
are	O
used	O
to	O
make	O
programs	O
more	O
efficient	O
without	O
changing	O
program	O
output	O
.	O
</s>
<s>
Although	O
checking	O
for	O
in	O
the	O
second	O
rule	O
may	O
appear	O
redundant	O
since	O
Prolog	B-Language
's	O
appearance	O
is	O
dependent	O
on	O
failing	O
before	O
,	O
otherwise	O
the	O
second	O
rule	O
would	O
not	O
be	O
evaluated	O
in	O
the	O
first	O
place	O
.	O
</s>
<s>
A	O
cut	O
that	O
is	O
not	O
a	O
green	B-Application
cut	I-Application
is	O
referred	O
to	O
as	O
a	O
cut	O
,	O
for	O
example	O
:	O
</s>
<s>
by	O
a	O
cut-and-paste	B-General_Concept
accident	O
)	O
or	O
moved	O
after	O
the	O
second	O
one	O
,	O
the	O
second	O
rule	O
will	O
be	O
broken	O
,	O
i.e.	O
,	O
it	O
will	O
not	O
guarantee	O
the	O
rule	O
.	O
</s>
