<s>
Proof-number	B-Algorithm
search	I-Algorithm
(	O
short	O
:	O
PN	O
search	O
)	O
is	O
a	O
game	O
tree	O
search	B-Application
algorithm	I-Application
invented	O
by	O
Victor	O
Allis	O
,	O
with	O
applications	O
mostly	O
in	O
endgame	O
solvers	O
,	O
but	O
also	O
for	O
sub-goals	O
during	O
games	O
.	O
</s>
<s>
first	O
player	O
wins	O
the	O
game	O
)	O
,	O
game	O
trees	O
of	O
two-person	O
perfect-information	O
games	O
can	O
be	O
mapped	O
to	O
an	O
and	B-Data_Structure
–	I-Data_Structure
or	I-Data_Structure
tree	I-Data_Structure
.	O
</s>
