<s>
In	O
computer	B-General_Concept
science	I-General_Concept
,	O
a	O
graph-structured	B-Data_Structure
stack	I-Data_Structure
(	O
GSS	O
)	O
is	O
a	O
directed	O
acyclic	O
graph	O
where	O
each	O
directed	O
path	O
represents	O
a	O
stack	B-Application
.	O
</s>
<s>
The	O
graph-structured	B-Data_Structure
stack	I-Data_Structure
is	O
an	O
essential	O
part	O
of	O
Tomita	B-Application
's	I-Application
algorithm	I-Application
,	O
where	O
it	O
replaces	O
the	O
usual	O
stack	B-Application
of	O
a	O
pushdown	B-Application
automaton	I-Application
.	O
</s>
<s>
In	O
the	O
following	O
diagram	O
,	O
there	O
are	O
four	O
stacks	B-Application
:	O
{7,3,1,0},	O
{7,4,1,0},	O
{7,5,2,0},	O
and	O
 { 8 , 6 , 2 , 0 } 	O
.	O
</s>
<s>
Another	O
way	O
to	O
simulate	O
nondeterminism	O
would	O
be	O
to	O
duplicate	O
the	O
stack	B-Application
as	O
needed	O
.	O
</s>
