<s>
Mac	B-Application
Hack	I-Application
is	O
a	O
computer	B-Application
chess	I-Application
program	O
written	O
by	O
Richard	O
D	O
.	O
Greenblatt	O
.	O
</s>
<s>
Also	O
known	O
as	O
Mac	O
Hac	O
and	O
The	O
Greenblatt	O
Chess	B-Application
Program	O
,	O
it	O
was	O
developed	O
at	O
the	O
Massachusetts	O
Institute	O
of	O
Technology	O
.	O
</s>
<s>
Mac	B-Application
Hack	I-Application
VI	I-Application
was	O
the	O
first	O
chess	B-Application
program	O
to	O
play	O
in	O
human	O
tournament	O
conditions	O
,	O
the	O
first	O
to	O
be	O
granted	O
a	O
chess	B-Application
rating	O
,	O
and	O
the	O
first	O
to	O
win	O
against	O
a	O
person	O
in	O
tournament	O
play	O
.	O
</s>
<s>
The	O
number	O
VI	O
refers	O
to	O
the	O
PDP-6	B-Device
machine	O
for	O
which	O
it	O
was	O
written	O
.	O
</s>
<s>
Greenblatt	O
was	O
inspired	O
to	O
write	O
Mac	B-Application
Hack	I-Application
upon	O
reading	O
MIT	O
Artificial	B-Application
Intelligence	I-Application
Memo	O
41	O
,	O
or	O
a	O
similar	O
document	O
describing	O
Kotok-McCarthy	B-Application
,	O
which	O
he	O
saw	O
while	O
visiting	O
Stanford	O
University	O
in	O
1965	O
.	O
</s>
<s>
A	O
good	O
chess	B-Application
player	O
,	O
he	O
was	O
inspired	O
to	O
make	O
improvements	O
at	O
MIT	O
in	O
1965	O
and	O
1966	O
.	O
</s>
<s>
In	O
about	O
2004	O
,	O
he	O
had	O
an	O
opportunity	O
to	O
tell	O
Alan	O
Kotok	O
that	O
searching	O
the	O
7	O
best	O
moves	O
at	O
each	O
of	O
the	O
first	O
two	O
plies	O
,	O
and	O
limiting	O
the	O
search	O
depth	O
to	O
two	O
would	O
have	O
done	O
better	O
than	O
the	O
default	O
widths	O
of	O
"	O
4	O
3	O
2	O
2	O
1	O
1	O
1	O
1	O
"	O
,	O
attempting	O
eight	O
plies	O
in	O
Kotok-McCarthy	B-Application
'	O
s	O
REPLYS	O
subroutine	O
which	O
generated	O
each	O
player	O
's	O
next	O
plausible	O
moves	O
.	O
</s>
<s>
Greenblatt	O
added	O
fifty	O
heuristics	B-Algorithm
that	O
reflected	O
his	O
knowledge	O
of	O
chess	B-Application
.	O
</s>
<s>
Mac	B-Application
Hack	I-Application
was	O
written	O
in	O
MIDAS	O
macro	O
assembly	B-Language
language	I-Language
on	O
the	O
PDP-6	B-Device
computer	O
DEC	O
donated	O
to	O
MIT	O
(	O
the	O
first	O
working	O
PDP-6	B-Device
,	O
serial	O
number	O
2	O
)	O
.	O
</s>
<s>
During	O
this	O
period	O
the	O
program	O
was	O
compiled	B-Language
about	O
two	O
hundred	O
times	O
.	O
</s>
<s>
By	O
the	O
time	O
it	O
was	O
published	O
in	O
1969	O
Mac	B-Application
Hack	I-Application
had	O
played	O
in	O
eighteen	O
tournaments	O
and	O
hundreds	O
of	O
complete	O
games	O
.	O
</s>
<s>
The	O
PDP-6	B-Device
became	O
an	O
honorary	O
member	O
of	O
the	O
Massachusetts	O
State	O
Chess	B-Application
Association	O
and	O
the	O
United	O
States	O
Chess	B-Application
Federation	O
,	O
a	O
requirement	O
for	O
playing	O
tournaments	O
.	O
</s>
<s>
In	O
1967	O
Mac	B-Application
Hack	I-Application
VI	I-Application
defeated	O
Ben	O
Landy	O
with	O
a	O
USCF	O
rating	O
of	O
1510	O
in	O
game	O
3	O
,	O
tournament	O
2	O
of	O
the	O
Massachusetts	O
State	O
Championship	O
.	O
</s>
<s>
Greenblatt	O
published	O
the	O
program	O
with	O
Donald	O
E	O
.	O
Eastlake	O
III	O
and	O
Stephen	O
D	O
.	O
Crocker	O
in	O
MIT	O
Artificial	B-Application
Intelligence	I-Application
Memo	O
174	O
and	O
recorded	O
some	O
games	O
there	O
.	O
</s>
<s>
Mac	B-Application
Hack	I-Application
played	O
by	O
teletype	O
,	O
was	O
ported	O
to	O
the	O
PDP-10	B-Device
and	O
was	O
the	O
first	O
computer	B-Application
chess	I-Application
program	O
to	O
be	O
widely	O
distributed	O
.	O
</s>
<s>
Mac	B-Application
Hack	I-Application
was	O
the	O
first	O
chess	B-Application
computer	I-Application
to	O
use	O
a	O
transposition	B-General_Concept
table	I-General_Concept
,	O
which	O
is	O
a	O
vital	O
optimization	O
in	O
game	O
tree	O
search	O
.	O
</s>
<s>
Greenblatt	O
and	O
Tom	O
Knight	O
went	O
on	O
to	O
advance	O
artificial	B-Application
intelligence	I-Application
and	O
build	O
the	O
Lisp	B-Operating_System
machine	I-Operating_System
in	O
1973	O
.	O
</s>
