<s>
In	O
computer	B-General_Concept
programming	I-General_Concept
,	O
an	O
opaque	B-General_Concept
predicate	I-General_Concept
is	O
a	O
predicate	B-Algorithm
,	O
an	O
expression	O
that	O
evaluates	O
to	O
either	O
"	O
true	O
"	O
or	O
"	O
false	O
"	O
,	O
for	O
which	O
the	O
outcome	O
is	O
known	O
by	O
the	O
programmer	O
a	O
priori	O
,	O
but	O
which	O
,	O
for	O
a	O
variety	O
of	O
reasons	O
,	O
still	O
needs	O
to	O
be	O
evaluated	O
at	O
run	B-Library
time	I-Library
.	O
</s>
<s>
Opaque	B-General_Concept
predicates	I-General_Concept
have	O
been	O
used	O
as	O
watermarks	B-General_Concept
,	O
as	O
they	O
will	O
be	O
identifiable	O
in	O
a	O
program	O
's	O
executable	O
.	O
</s>
<s>
They	O
can	O
also	O
be	O
used	O
to	O
prevent	O
an	O
overzealous	O
optimizer	B-Application
from	O
optimizing	O
away	O
a	O
portion	O
of	O
a	O
program	O
.	O
</s>
<s>
Another	O
use	O
is	O
in	O
obfuscating	O
the	O
control	O
or	O
dataflow	B-Application
of	O
a	O
program	O
to	O
make	O
reverse	O
engineering	O
harder	O
.	O
</s>
