<s>
Well-formed	B-General_Concept
Petri	I-General_Concept
nets	I-General_Concept
are	O
a	O
Petri	B-Operating_System
net	I-Operating_System
class	O
jointly	O
elaborated	O
between	O
the	O
University	O
of	O
Paris	O
6	O
(	O
Université	O
P	O
.	O
&	O
M	O
.	O
Curie	O
)	O
and	O
the	O
University	O
of	O
Torino	O
in	O
the	O
early	O
1990s	O
.	O
</s>
<s>
A	O
symbolic	O
state	O
is	O
a	O
state	O
representing	O
several	O
concrete	O
states	O
in	O
the	O
state	O
space	O
of	O
the	O
system	O
described	O
by	O
the	O
Petri	B-Operating_System
net	I-Operating_System
.	O
</s>
