<s>
An	O
event	B-Application
segment	I-Application
is	O
a	O
special	O
class	O
of	O
the	O
constant	O
segment	O
with	O
a	O
constraint	O
in	O
which	O
the	O
constant	O
segment	O
is	O
either	O
one	O
of	O
a	O
timed	O
event	O
or	O
a	O
null-segment	O
.	O
</s>
<s>
The	O
event	B-Application
segments	I-Application
are	O
used	O
to	O
define	O
Timed	B-Application
Event	I-Application
Systems	I-Application
such	O
as	O
DEVS	B-Application
,	O
timed	B-Application
automata	I-Application
,	O
and	O
timed	O
petri	O
nets	O
.	O
</s>
<s>
A	O
unit	O
event	B-Application
segment	I-Application
is	O
either	O
a	O
null	O
event	B-Application
segment	I-Application
or	O
a	O
timed	O
event	O
.	O
</s>
<s>
Given	O
an	O
event	O
set	O
,	O
concatenation	O
of	O
two	O
unit	O
event	B-Application
segments	I-Application
over	O
and	O
over	O
is	O
denoted	O
by	O
whose	O
time	O
interval	O
is	O
,	O
and	O
implies	O
.	O
</s>
