<s>
Otter	B-Application
is	O
an	O
automated	B-Application
theorem	I-Application
prover	I-Application
developed	O
by	O
William	O
McCune	O
at	O
Argonne	O
National	O
Laboratory	O
in	O
Illinois	O
.	O
</s>
<s>
Otter	B-Application
was	O
the	O
first	O
widely	O
distributed	O
,	O
high-performance	O
theorem	O
prover	O
for	O
first-order	O
logic	O
,	O
and	O
it	O
pioneered	O
a	O
number	O
of	O
important	O
implementation	O
techniques	O
.	O
</s>
<s>
Otter	B-Application
is	O
an	O
acronym	O
for	O
Organized	O
Techniques	O
for	O
Theorem-proving	O
and	O
Effective	O
Research	O
.	O
</s>
<s>
Otter	B-Application
is	O
based	O
on	O
resolution	O
and	O
paramodulation	O
,	O
constrained	O
by	O
term	O
orderings	O
similar	O
to	O
those	O
in	O
the	O
superposition	O
calculus	O
.	O
</s>
<s>
Otter	B-Application
also	O
pioneered	O
the	O
use	O
of	O
efficient	O
term	B-Application
indexing	I-Application
techniques	O
to	O
speed	O
up	O
the	O
search	O
for	O
inference	O
partners	O
in	O
large	O
clause	O
sets	O
.	O
</s>
<s>
Otter	B-Application
has	O
been	O
very	O
stable	O
for	O
a	O
number	O
of	O
years	O
but	O
is	O
no	O
longer	O
actively	O
developed	O
.	O
</s>
<s>
A	O
successor	O
to	O
Otter	B-Application
is	O
Prover9	B-Application
.	O
</s>
<s>
According	O
to	O
Wos	O
and	O
Pieper	O
,	O
OTTER	B-Application
is	O
written	O
in	O
approximately	O
28,000	O
lines	O
of	O
C	O
programming	O
language	O
.	O
</s>
