Empty
(
X
) for
G
expr
3
: Example
Empty
(
i
)
:=
Æ
Empty
(
+
)
:=
Æ
Empty
(
*
)
:=
Æ
Empty
(
(
)
:=
Æ
Empty
(
)
)
:=
Æ
19/57
Initialization:
Empty
(
E
)
:=
Æ
Empty
(
E
’
)
:=
{
e
}
Empty
(
T
)
:=
Æ
Empty
(
T
’
)
:=
{
e
}
Empty
(
F
)
:=
Æ
•
No
Empty
set can be changed.
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
}