<s>
HiLog	B-Language
is	O
a	O
programming	O
logic	O
with	O
higher-order	O
syntax	O
,	O
which	O
allows	O
arbitrary	O
terms	O
to	O
appear	O
in	O
predicate	O
and	O
function	O
positions	O
.	O
</s>
<s>
However	O
,	O
the	O
model	O
theory	O
of	O
HiLog	B-Language
is	O
first-order	O
.	O
</s>
<s>
Although	O
syntactically	O
HiLog	B-Language
strictly	O
extends	O
first	O
order	O
logic	O
,	O
HiLog	B-Language
can	O
be	O
embedded	O
into	O
this	O
logic	O
.	O
</s>
<s>
HiLog	B-Language
was	O
first	O
described	O
in	O
1989	O
.	O
</s>
<s>
The	O
XSB	B-Language
system	O
parses	O
HiLog	B-Language
syntax	O
,	O
but	O
the	O
integration	O
of	O
HiLog	B-Language
into	O
XSB	B-Language
is	O
only	O
partial	O
.	O
</s>
<s>
In	O
particular	O
,	O
HiLog	B-Language
is	O
not	O
integrated	O
with	O
the	O
XSB	B-Language
module	O
system	O
.	O
</s>
<s>
A	O
full	O
implementation	O
of	O
HiLog	B-Language
is	O
available	O
in	O
the	O
Flora-2	B-Language
system	O
.	O
</s>
<s>
It	O
has	O
been	O
shown	O
that	O
HiLog	B-Language
can	O
be	O
embedded	O
into	O
first-order	O
logic	O
through	O
a	O
fairly	O
simple	O
transformation	O
.	O
</s>
<s>
The	O
Framework	O
for	O
Logic-Based	O
Dialects	O
(	O
RIF-FLD	O
)	O
of	O
the	O
Rule	B-Language
Interchange	I-Language
Format	I-Language
(	O
RIF	O
)	O
is	O
largely	O
based	O
on	O
the	O
ideas	O
underlying	O
HiLog	B-Language
and	O
F-logic	B-Language
.	O
</s>
<s>
In	O
all	O
the	O
examples	O
below	O
,	O
capitalized	O
symbols	O
denote	O
variables	O
and	O
the	O
comma	O
denotes	O
logical	O
conjunction	O
,	O
as	O
in	O
most	O
logic	B-Language
programming	I-Language
languages	I-Language
.	O
</s>
<s>
It	O
defines	O
a	O
LISP-like	O
mapping	O
operator	O
,	O
which	O
applies	O
to	O
an	O
arbitrary	O
binary	O
predicate	O
.	O
</s>
<s>
The	O
third	O
example	O
shows	O
that	O
the	O
Prolog	B-Language
meta-predicate	O
call/1	O
can	O
be	O
expressed	O
in	O
HiLog	B-Language
in	O
a	O
natural	O
way	O
and	O
without	O
the	O
use	O
of	O
extra-logical	O
features	O
.	O
</s>
