•
if
A
®
X
1
X
2
…
X
k
-1
X
k
…
X
n
Î
P
then
Previous Algorithm: Illustration
1)
for each
a
Î
T
:
First
(
a
) := {
a
} because
a
Þ
0
a
2)
for each
A
Î
N
:
First
(
A
) :=
Æ
(inicialization)
e
a
Î
First
(
X
k
)
a
Î
First
(
A
)
e
e
e
…
3b) if
Empty
(
X
i
) = {
e
} for all
i
= 1,…,
k
-1, where
k
<
n
then
add all symbols from
First
(
X
k
) to
First
(
A
):
A
X
1
X
2
X
k
-1
…
X
n
X
k
…
3b:
3)
Apply the following rules until no
First
set or
Empty
set can be changed:
…
a
21/57
a
Î
First
(
X
k
)
a
Î
First
(
A
)
…
a
3a:
A
X
1
X
2
…
X
n
3a)
add all symbols from
First
(
X
1
) to
First
(
A
)