•
Input:
G
= (
N
,
T
,
P
,
S
)
without
e
-rules
•
Output:
First
(
X
) for every
X
Î
N
È
T
•
Method:
•
for e
ach
a
Î
T
:
First
(
a
) := {
a
}
•
Apply the following rule until no
First
set
can be changed:
•
if
A
®
X
1
X
2
…
X
n
Î
P
, then add
First
(
X
1
) to
First
(
A
)
Algorithm
:
First
(
X
)
1)
for e
ach
a
Î
T
:
First
(
a
) := {
a
}
because
a
Þ
0
a
Illustration:
a
Î
First
(
A
)
A
X
1
X
2
…
X
n
2)
a
Î
First
(
X
1
)
…
a
7/57