<s>
An	O
and	B-Data_Structure
–	I-Data_Structure
or	I-Data_Structure
tree	I-Data_Structure
is	O
a	O
graphical	O
representation	O
of	O
the	O
reduction	O
of	O
problems	O
(	O
or	O
goals	O
)	O
to	O
conjunctions	O
and	O
disjunctions	O
of	O
subproblems	O
(	O
or	O
subgoals	O
)	O
.	O
</s>
<s>
The	O
and-or	B-Data_Structure
tree	I-Data_Structure
:	O
</s>
<s>
the	O
associated	O
and-or	B-Data_Structure
tree	I-Data_Structure
is	O
a	O
set	O
of	O
labelled	O
nodes	O
such	O
that	O
:	O
</s>
<s>
An	O
and-or	B-Data_Structure
tree	I-Data_Structure
specifies	O
only	O
the	O
search	O
space	O
for	O
solving	O
a	O
problem	O
.	O
</s>
<s>
Different	O
search	B-Algorithm
strategies	I-Algorithm
for	O
searching	O
the	O
space	O
are	O
possible	O
.	O
</s>
<s>
The	O
methods	O
used	O
for	O
generating	O
and-or	B-Data_Structure
trees	I-Data_Structure
are	O
propositional	O
logic	B-Language
programs	I-Language
(	O
without	O
variables	O
)	O
.	O
</s>
<s>
In	O
the	O
case	O
of	O
logic	B-Language
programs	I-Language
containing	O
variables	O
,	O
the	O
solutions	O
of	O
conjoint	O
sub-problems	O
must	O
be	O
compatible	O
.	O
</s>
<s>
Subject	O
to	O
this	O
complication	O
,	O
sequential	O
and	O
parallel	O
search	B-Algorithm
strategies	I-Algorithm
for	O
and-or	B-Data_Structure
trees	I-Data_Structure
provide	O
a	O
computational	O
model	O
for	O
executing	O
logic	B-Language
programs	I-Language
.	O
</s>
<s>
And	B-Data_Structure
–	I-Data_Structure
or	I-Data_Structure
trees	I-Data_Structure
can	O
also	O
be	O
used	O
to	O
represent	O
the	O
search	O
spaces	O
for	O
two-person	O
games	O
.	O
</s>
<s>
For	O
solving	O
game	O
trees	O
with	O
proof-number	B-Algorithm
search	I-Algorithm
family	O
of	O
algorithms	O
,	O
game	O
trees	O
are	O
to	O
be	O
mapped	O
to	O
and-or	B-Data_Structure
trees	I-Data_Structure
.	O
</s>
