First
(
X
1
X
2
…
X
n
): Example
25/57
Empty
(
E
)
:=
Æ
Empty
(
E
’
)
:=
{
e
}
Empty
(
T
)
:=
Æ
Empty
(
T
’
)
:=
{
e
}
Empty
(
F
)
:=
Æ
First
(
E
)
:=
{
i
,
(
}
First
(
E
’
)
:=
{
+
}
First
(
T
)
:=
{
i
,
(
}
First
(
T
’
)
:=
{
*
}
First
(
F
)
:=
{
i
,
(
}
G
expr
3
= (
N
,
T
,
P
,
E
), where:
N
= {
E
,
F
,
T
},
T
= {
i
,
+
,
*
,
(
,
)
},
P
= {
1
:
E
®
T
E
’
,
2
:
E
’
®
+
TE
’
,
3
:
E
’
®
e
,
4
:
T
®
FT
’
5
:
T
’
®
*
FT
’
,
6
:
T
’
®
e
,
7
:
F
®
(
E
)
,
8
:
F
®
i
}
Set
Empty
&
First
for all
X
Î
N
:
Task:
First
(
E
’
T
’
FET
)
1)
First
(
E
’
T
’
FET
) :=
First
(
E
’
) = {
+
}
2)
First
(
E
’
T
’
FET
):
add
First
(
T
’
) = {
*
}
to
First
(
E
’
T
’
FET
)
Empty
(
E
’
)
=
{
e
}
3)
First
(
E
’
T
’
F
ET
):
add
First
(
F
) =
{
i
,
(
}
to
First
(
E
’
T
’
FET
)
Empty
(
E
’
)
=
Empty
(
T
’
)
=
{
e
}
Summary:
First
(
E
’
T
’
FET
) =
{
+
,
*
,
i
,
(
}