First
(
X
)
for
G
expr
3
: Example
F
®
i
Î
P
:
add
First
(
i
) =
{
i
}
to
First
(
F
)
F
®
(
E
)
Î
P
:
add
First
(
(
) =
{
(
}
to
First
(
F
)
Summary:
First
(
F
) = {
i
,
(
}
T
’
®
*
FT
’
Î
P
:
add
First
(
*
) =
{
*
}
to
First
(
T
’
)
Summary:
First
(
T
’
) = {
*
}
T
®
FT
’
Î
P
:
add
First
(
F
) =
{
i
,
(
}
to
First
(
T
)
Summary:
First
(
T
)
= {
i
,
(
}
E
’
®
+
TE
’
Î
P
:
add
First
(
+
) =
{
+
}
to
First
(
E
’
)
Summary:
First
(
E
’
) = {
+
}
E
®
TE
’
Î
P
:
add
First
(
T
) =
{
i
,
(
}
to
First
(
E
)
Summary:
First
(
E
)
= {
i
,
(
}
22/57
First
(
i
)
:= {
i
}
First
(
+
)
:= {
+
}
First
(
*
)
:= {
*
}
First
(
(
)
:= {
(
}
First
(
)
)
:= {
)
}
Initialization:
First
(
E
)
:=
Æ
First
(
E
’
)
:=
Æ
First
(
T
)
:=
Æ
First
(
T
’
)
:=
Æ
First
(
F
)
:=
Æ
•
No
First
set can be changed.