1.2
Functional Diagrams and Function Symbols*
J. E. JAMISON
(2003)
The purpose of this section is to help the reader establish a
uniform means of depicting and identifying mainly digitalbased application software functions used for measurement,
monitoring, and control. It is done by presenting a designation system including graphic symbols and identification codes
as well as functional diagramming techniques that were
formerly known as the Scientific Apparatus Manufacturers’
Association (SAMA) system.
It must be noted that a significant part of this section has
been extracted from the revision work of the ISA SP5.1
subcommittee, and much of it has been based on draft working documents being utilized at the time of this writing,
documents with which one of the authors has been actively
involved. Other portions of this section are based on the
author’s experience in the industry and are not any part of
the SP5.1 subcommittee proposed forthcoming revision.
A disclaimer to any future ISA standards documents is
hereby stated: The reader is cautioned that the draft ISA
document that provided much of the information in this
section has not been approved as of the time of this writing.
It cannot be presumed to reflect the position of ISA or any
other committee, society, or group.
The intent is to pass along to the reader the best and latest
thinking on this subject at this point in time.
ISA FUNCTIONAL DIAGRAMMING (EX-SAMA)*
Instrument and Control Systems Functional Diagramming
Symbol tables are given for use in preparing instrument and
control loop functional diagrams, which are not normally
shown on process flow diagrams (PFDs) and piping and instrument diagrams (P&IDs). They are used to depict monitoring
and control loops in functional instrument diagrams, functional
logic diagrams, application software diagrams, sketches, and
text. They shall be prepared from the following:
a) Instrument line symbols
b) Instrument functional diagramming symbols
c) Mathematical function block symbols
Equivalent P&ID Loop, Functional Instrument
and Electrical Diagrams
See statement of permission in the footnote below.
a) P&ID loop schematic:
LT
∗71
LSH
∗01
LIC
∗01
LSL
∗01
Start
HS
∗
01B-1
SP
FT
Stop
HS
∗01B-2
H-O-A
∗01
FIC
∗01
HS
∗01A
FV
∗01
P
∗01
FO
* Used with permission of the Instrumentation, Systems and Automation Society.
31
© 2003 by Béla Lipták
32
General Considerations
b) Functional instrument diagram:
LT
FT
*01
*01
A
N
D
H/ L
A
K
HS*1A
I
A
N
D
Auto
OR
NOT
NOT
K
I
HS*1B-1
T
A
T
HS*1B-2
A
A
N
D
Start
Start Pump
A
N
D
Stop
Overload
A
N
D
OR
S
NOT
R
Reset
F(x)
c) Electrical schematic diagram:
START
HS-∗01B-1
M1
STOP
HS-∗01B-2
LSL-∗01
H
OL
HS-∗01A
M
0
M2
LSH-∗01
Note: There is no equivalent electrical schematic for the
process control instrumentation.
Functional Diagramming Symbol Tables*
The symbols used in Table 1.2a are not normally used on
P&IDs but are used to diagram control systems at the
*The symbols have been extracted by ISA, with permission, from Scientific
Apparatus Manufacturers’ Association SAMA Standard PMC 22.1–1981,
Functional Diagramming of Instrument and Control Systems, which is no
longer supported by SAMA.
© 2003 by Béla Lipták
hardware and function level for configuration and other
purposes.
The symbols in Table 1.2b are never used in P&IDs and
are used to help document and diagram logic control designs
and narratives. The present standard ISA S5.2 (ANSI/ISAS5.2–1976 [R1992]) is now being revised and rolled into the
new ANSI/ISA-5.01.01 standard as proposed in the current
(as of this writing) Draft 4. Symbols, truth tables, definitions,
and graphs used in this section are in accordance with Draft
4 and are very different from S5.2. They are given here to
illustrate the latest thinking in this area, including expanded
1.2 Functional Diagrams and Function Symbols
33
TABLE 1.2a
Functional Diagramming Symbols—Instrument and Mathematical Functions (proposed for the next revision
of ISA S5.1 [now ANSI/ISA-5.01.01] at the time of this writing)
No.
Symbol
Description
01
Measuring device
Input device
Readout device
Output device
Symbols from Tables 1.1h through 1.1k may be used
02
Automatic controller
Single-mode controller
Discrete device driver
Insert function symbols, as required to define controller algorithm, from Table 1.2c
Use for vertical diagramming
03
Automatic controller
Two-mode controller
Insert function symbols, as required to define controller algorithm, from Table 1.2c
Use for vertical diagramming
04
Automatic controller
Three-mode controller
Insert function symbols, as required to define controller algorithm, from Table 1.2c
Use for vertical diagramming
05
Automatic signal processor
Insert function symbol from Table 1.2c
Use for vertical diagramming
06
Automatic controller
Two-mode controller
Insert function symbols, as required to define controller algorithm, from Table 1.2c
Use for horizontal diagramming
07
Automatic controller
Two-mode controller
Insert function symbols, as required to define controller algorithm, from Table 1.2c
Use for horizontal diagramming
08
Automatic signal processor
Insert function symbol from Table 1.2c
Use for horizontal diagramming
May be rotated 90°
09
Final control element
Control valve
Insert function symbol identifier from Table 1.2c (no. 14)
10
Final control element with positioner
Control valve with positioner
Insert function symbol identifier from Table 1.2c (no.14)
11
Manual signal processor
(*) = A, adjustable signal generator
(*) = T, signal transfer
*
12
Manual auto station
A
T
See statement of permission on page 31.
timing functions. Application information and examples on
the use of the binary symbols are given in Section 1.12, Binary
Logic Diagrams, and they use the current standard ANSI/ISAS5.2–1976 (R1992).
© 2003 by Béla Lipták
Binary logic switching and memory functions are
used in analog or sequential control schemes. In truth
tables and graphs, logic one (1) is true and logic zero
(0) is false.
34
General Considerations
TABLE 1.2b
Instrument and Control System Functional Diagramming Symbols—Binary Logic, Memory, and Time Functions (proposed for the next
revision of ISA S5.1 [now ANSI/ISA-5.01.01] at the time of this writing)
No.
Symbol/Truth Table
Definition/Graph
01
A
B
C
AND gate.
Output is true only if all inputs are true.
A
N
D
O
x
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
A
B
C
x
O
0
1
0
0
0
1
1
1
0
0
0
1
1
1
0
1
0
0
1
0
0
1
0
0
1
1
0
1
1
0
1
1
0
0
0
1
0
0
1
0
1
0
1
1
0
1
1
1
0
0
0
0
1
0
0
1
0
1
1
0
1
1
1
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
02
1
0
A
B
C
X
O
t
1
2
3
4
5
6
7
8
9
10
11
12 13
14
15
16
OR gate.
Output is true if any input true.
A
B
C
OR
O
x
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
A
0
1
0
0
0
1
1
1
0
0
0
1
1
1
0
1
© 2003 by Béla Lipták
B
0
0
1
0
0
1
0
0
1
1
0
1
1
0
1
1
C
0
0
0
1
0
0
1
0
1
0
1
1
0
1
1
1
x
0
0
0
0
1
0
0
1
0
1
1
0
1
1
1
1
O
0
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
0
A
B
C
X
O
t
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
1.2 Functional Diagrams and Function Symbols
35
TABLE 1.2b Continued
Instrument and Control System Functional Diagramming Symbols—Binary Logic, Memory, and Time Functions (proposed for the next
revision of ISA S5.1 [now ANSI/ISA-5.01.01] at the time of this writing)
No.
Symbol/Truth Table
03
A
B
C
≥n
O
Definition/Graph
Qualified OR gate with greater than or equal to qualifications.
Output equals “1” if number of inputs equal to “1” are greater than or equal to “n” inputs.
Truth table and graph are for “n” equals 2.
x
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
A
0
1
0
0
0
1
1
1
0
0
0
1
1
1
0
1
B
0
0
1
0
0
1
0
0
1
1
0
1
1
0
1
1
C
0
0
0
1
0
0
1
0
1
0
1
1
0
1
1
1
x
0
0
0
0
1
0
0
1
0
1
1
0
1
1
1
1
O
0
0
0
0
0
1
1
1
1
1
1
1
1
1
1
1
04
A
B
C
>n
O
1
0
A
B
C
X
O
t
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Qualified OR gate with greater than qualifications.
Output equals “1” if number of inputs equal to “1” are greater but not equal to “n” inputs.
Truth table and graph are for “n” equals 2.
x
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
A
0
1
0
0
0
1
1
1
0
0
0
1
1
1
0
1
B
0
0
1
0
0
1
0
0
1
1
0
1
1
0
1
1
C
0
0
0
1
0
0
1
0
1
0
1
1
0
1
1
1
x
0
0
0
0
1
0
0
1
0
1
1
0
1
1
1
1
O
0
0
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
0
A
B
C
X
O
t
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
(Continued)
© 2003 by Béla Lipták
36
General Considerations
TABLE 1.2b Continued
Instrument and Control System Functional Diagramming Symbols—Binary Logic, Memory, and Time Functions (proposed for the next
revision of ISA S5.1 [now ANSI/ISA-5.01.01] at the time of this writing)
No.
Symbol/Truth Table
05
A
B
C
≤n
O
Definition/Graph
Qualified OR gate with less than or equal to qualifications.
Output equals “1” if number of inputs equal to “1” are less than or equal to “n” inputs.
Truth table and graph are for “n” equals 2.
x
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
A
0
1
0
0
0
1
1
1
0
0
0
1
1
1
0
1
B
0
0
1
0
0
1
0
0
1
1
0
1
1
0
1
1
C
0
0
0
1
0
0
1
0
1
0
1
1
0
1
1
1
x
0
0
0
0
1
0
0
1
0
1
1
0
1
1
1
1
O
0
1
1
1
1
1
1
1
1
1
1
0
0
0
0
0
06
A
B
C
<n
O
1
0
A
B
C
X
O
t
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Qualified OR gate with less than qualifications.
Output equals “1” if number of inputs equal to “1” are less but not equal to “n” inputs.
Truth table and graph are for “n” equals 2.
x
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
© 2003 by Béla Lipták
A
0
1
0
0
0
1
1
1
0
0
0
1
1
1
0
1
B
0
0
1
0
0
1
0
0
1
1
0
1
1
0
1
1
C
0
0
0
1
0
0
1
0
1
0
1
1
0
1
1
1
x
0
0
0
0
1
0
0
1
0
1
1
0
1
1
1
1
O
0
1
1
1
1
0
0
0
0
0
0
0
0
0
0
0
1
0
A
B
C
X
O
t
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
1.2 Functional Diagrams and Function Symbols
37
TABLE 1.2b Continued
Instrument and Control System Functional Diagramming Symbols—Binary Logic, Memory, and Time Functions (proposed for the next
revision of ISA S5.1 [now ANSI/ISA-5.01.01] at the time of this writing)
No.
Symbol/Truth Table
07
A
B
C
=n
O
Definition/Graph
Qualified OR gate with equal to qualifications.
Output equals “1” if inputs equal to “1” are equal to “n” inputs.
Truth table and graph are for “n” equals 2.
x
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
08
A
0
1
0
0
0
1
1
1
0
0
0
1
1
1
0
1
A
B
C
B
0
0
1
0
0
1
0
0
1
1
0
1
1
0
1
1
C
0
0
0
1
0
0
1
0
1
0
1
1
0
1
1
1
x
0
0
0
0
1
0
0
1
0
1
1
0
1
1
1
1
≠n
O
0
0
0
0
0
1
1
1
1
1
1
0
0
0
0
0
O
1
0
A
B
C
X
O
t
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Qualified OR gate with not equal to qualifications.
Output equals “1” if inputs equal to “1” are not equal to “n” inputs.
Truth table and graph are for “n” equals 2.
x
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
A
0
1
0
0
0
1
1
1
0
0
0
1
1
1
0
1
B
0
0
1
0
0
1
0
0
1
1
0
1
1
0
1
1
C
0
0
0
1
0
0
1
0
1
0
1
1
0
1
1
1
x
0
0
0
0
1
0
0
1
0
1
1
0
1
1
1
1
O
0
1
1
1
1
0
0
0
0
0
0
1
1
1
1
1
1
0
A
B
C
X
O
t
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
(Continued)
© 2003 by Béla Lipták
38
General Considerations
TABLE 1.2b Continued
Instrument and Control System Functional Diagramming Symbols—Binary Logic, Memory, and Time Functions (proposed for the next
revision of ISA S5.1 [now ANSI/ISA-5.01.01] at the time of this writing)
No.
Symbol/Truth Table
09
NOT
A
A
1
0
O
O
0
1
Definition/Graph
NOT gate.
Output is false if input is true.
Output is true if input is false.
A
1
0
O
1
0
t
1
10
A
S
C
B
R
D
1
2
3
4
5
6
7
8
A
0
1
0
0
0
1
0
1
B
0
0
0
1
0
1
0
1
C
0
1
1
0
0
1
1
0
D
1
0
0
1
1
0
0
1
2
3
4
A
So
C
B
R
D
1
2
3
4
5
6
7
8
A
0
1
0
0
0
1
0
1
B
0
0
0
1
0
1
0
1
C
0
1
1
0
0
1
1
1
D
1
0
0
1
1
0
0
0
7
8
9
10
11
12
13
14
15
16
1
0
B
C
D
t
2
3
4
5
6
7
8
Set dominant memory (“So dominant”).
Outputs C and D are always opposite.
If input A equals “1”, then output C equals “1”, and D equals “0”.
If input A changes to “0”, output C remains “1” until input B equals “1”, then output C equals “1”, and
D equals “0”.
If input B equals “1”, then output D equals “1”, and C equals “0”.
If input B changes to “0”, output D remains “1” until input A equals “1”, then output D equals “1”, and
C equals “0”.
If inputs A and B are simultaneously equal to “1”, then output C equals “1”, and D equals “0”.
1
0
A
B
C
D
t
1
© 2003 by Béla Lipták
6
A
1
11
5
Basic memory.
Outputs C and D are always opposite.
If input A equals “1”, then output C equals “1”, and D equals “0”.
If input A changes to “0”, output C remains “1” until input B equals “1”, then C equals “1”, and D equals “0”.
If input B equals “1”, then output D equals “1”, and C equals “0”.
If input B changes to “0”, output D remains “1” until input A equals “1”, then D equals “1”, and C equals “0”.
If inputs A and B are simultaneously equal to “1”, then outputs C and D change state.
2
3
4
5
6
7
8
1.2 Functional Diagrams and Function Symbols
39
TABLE 1.2b Continued
Instrument and Control System Functional Diagramming Symbols—Binary Logic, Memory, and Time Functions (proposed for the next
revision of ISA S5.1 [now ANSI/ISA-5.01.01] at the time of this writing)
No.
12
Symbol/Truth Table
A
S
C
B
Ro
D
1
2
3
4
5
6
7
8
A
0
1
0
0
0
1
0
1
B
0
0
0
1
0
1
0
1
C
0
1
1
0
0
0
0
0
Definition/Graph
Reset dominant memory (“Ro dominant”).
Outputs C and D are always opposite.
If input A equals “1”, then output C equals “1”, and D equals “0”.
If input A changes to “0”, output C remains “1” until input B equals “1”, then output C equals “1”, and
D equals “0”.
If input B equals “1”, then output D equals “1”, and C equals “0”.
If input B changes to “0”, output D remains “1” until input A equals “1”, then output D equals “1”, and
C equals “0”.
If inputs A and B are simultaneously equal to “1”, then C equals “0”, and D equals “1”.
D
1
0
0
1
1
1
1
1
1
0
A
B
C
D
t
1
13
I
t
PD
O
2
3
4
5
6
7
8
Pulse duration, fixed.
Output O changes from “0” to “1” and remains “1” for prescribed time duration “t” when input “I” changes
from “0” to “1”.
NONE
1
0
I
O
t
t
t
14
I
t
DT
O
Off-time delay.
Output O changes from “0” to “1” when input “I” changes from “0” to “1”.
Output O changes from “1” to “0” after input I changes from “1” to “0” and has been equal to “0” for
time duration “t”.
NONE
1
0
I
O
t
t
t
(Continued)
© 2003 by Béla Lipták
40
General Considerations
TABLE 1.2b Continued
Instrument and Control System Functional Diagramming Symbols—Binary Logic, Memory, and Time Functions (proposed for the next
revision of ISA S5.1 [now ANSI/ISA-5.01.01] at the time of this writing)
No.
Symbol/Truth Table
15
I
t
GT
O
R
Definition/Graph
On-time delay.
Output O changes from “0” to “1” after input “I” changes from “0” to “1” and “I” remains “1” for prescribed
time duration “t”.
Output O remains “1” until
a. Input “I” changes to “0”.
b. Reset R changes to “1”.
NONE
1
0
I
O
t
t
t
R
16
I
t
LT
O
R
t
Pulse duration, variable.
Output O changes from “0” to “1” when input “I” changes from “0” to “1”.
Output O changes from “1” to “0” when
a. Input “I” has equaled “1” for time duration “t”.
b. Input “I” changes from “1” to “0”.
c. Reset R changes to “1”.
NONE
1
0
I
O
R
See statement of permission on page 31.
© 2003 by Béla Lipták
t
t
t
t
1.2 Functional Diagrams and Function Symbols
41
TABLE 1.2c
Mathematical Function Block Symbols (proposed for the next revision of ISA S5.1 [now ANSI/ISA-5.01.01] at the time of this writing)
No.
01
Symbol/Function
Equation/Graph
Definition
Output equals the algebraic sum of inputs.
M = X 1 + X 2 … .+ X n
Σ
X
Xn
M
X1
Summation
X2
t
02
Σ/n
M = X1 + X2
…. +
t
Output equals the algebraic sum of the inputs divided by number
of inputs.
X n/n
X
M
X1
X2
X3
Average
t
t
03
Output equals the difference between two inputs.
M = X1 − X2
∆
X
X1
M
X2
Difference
t
04
t
Output equals the product of the two inputs.
M = X1 X2
X
X1
X
M
X2
Multiplication
t1
05
÷
t1
t
t
Output equals the quotient of the two inputs.
M = X1 / X2
X1
X
M
X2
Division
t1
06
2
X
M=X
t1
t
t
Output is equal to the square of the input.
2
X
M
Square
t
t
07
X
n
M= X
Output is equal to the nth power of the input.
n
X
M
Exponential
t
t
(Continued)
© 2003 by Béla Lipták
42
General Considerations
TABLE 1.2c Continued
Mathematical Function Block Symbols (proposed for the next revision of ISA S5.1 [now ANSI/ISA-5.01.01] at the time of this writing)
No.
08
Symbol/Function
√
Equation/Graph
X
M=
Definition
Output is equal to the square root of the input.
M
X
Square Root
t
t
09
n
√
n
M=
X
Output is equal to the nth root of the input.
X
M
nth Root
t
10
K or P
t
Output is proportional to the input.
Replace “K” with “1:1” for volume boosters.
Replace “K” with “2:1”, ‘3:1”, etc. for integer gains.
M = KX
X
M
Proportional
t1
11
-K or -P
t
t
t1
M = −KX
t1
Output is inversely proportional to the input.
t
X
Reverse
Proportional
M
t
t1
12
∫ or I
M = (1/TI )
X
∫
Output varies with the magnitude and time duration of the input.
Output is proportional to the time integral of the input.
TI, the integral time constant.
X dt
M
Integral
t1
13
d/dt or D
t2
t
t1
t2
t
Output is proportional to the time rate of change of the input.
TD , derivative time constant.
M = T D (dX/dt)
X
M
Derivative
t1
14
ƒ(X)
t
t1
t
Output is a nonlinear or unspecified function of the input.
Function is defined in note or other text.
M = ƒ (X)
X
M
Unspecified
Function
t
© 2003 by Béla Lipták
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1.2 Functional Diagrams and Function Symbols
43
TABLE 1.2c Continued
Mathematical Function Block Symbols (proposed for the next revision of ISA S5.1 [now ANSI/ISA-5.01.01] at the time of this writing)
No.
15
Symbol/Function
ƒ(t)
Equation/Graph
Definition
Output equals a nonlinear or unspecified time function times the
input.
Output is a nonlinear or unspecified time function.
M = Xƒ(t)
X
M
Time Function
t1
16
>
t
t1
t
Output equals greater of two or more inputs.
M = X 1 for X 1 ≥ X 2 , M = X 2 for X 1 ≤ X 2
X
X1
M
X2
High Select
t1
17
<
M = X 1 for X 1 ≤
X
t
t
t1
Output equals lesser of two or more inputs.
X 2 , M = X 2 for X 1 ≥ X 2
X1
M
X2
Low Select
t1
18
>
t
t
t1
Output equals the lower of the input or high limit values.
M = X1 for X1 ≤ H, M = X2 for X1 ≥ H
X
X
M
H
High Limit
t
t1
19
<
t1
t
Output equals the higher of the input or low limit values.
M = X1 for X1 ≥ L, M = X2 for X1 ≤ L
X
X
M
H
Low Limit
t1
20
V
Velocity Limiter
t
t1
t
Output equals input as long as the input rate of change does not
exceed the limit value that establishes the output rate of change
until the output again equals the input.
dM/dt = dX/dt (dX/dt ≤ H, M = X)
dM/dt = H (dX/dt ≥ H, M ≠ X)
dX/dt>H
X
dM/dt=H
M
t1
t2
t
t1
t2
t
(Continued)
© 2003 by Béla Lipták
44
General Considerations
TABLE 1.2c Continued
Mathematical Function Block Symbols (proposed for the next revision of ISA S5.1 [now ANSI/ISA-5.01.01] at the time of this writing)
No.
21
Symbol/Function
Equation/Graph
Definition
Output is equal to input plus an arbitrary value.
M=X+b
+
X
M
b
Positive Bias
t
X
t
M
b
t
22
t
Output is equal to input minus an arbitrary value.
M=X−b
−
X
M
b
Negative Bias
t
X
t
M
b
t
t
25
I = P, P = I, etc.
∗/∗
I
P
Conversion
t
26
∗H
Output state is dependent on the value of the input.
Output changes state when the input is equal to or higher than an
arbitrary high limit.
(State 1) M = 0 @ X < H
(State 2) M = 1 @ X ≥ Η
X
High Signal
Monitor
X
State
1
H
t1
27
∗L
Low Signal
Monitor
t
State
2
t1
Output state is dependent on the value of the input.
Output changes state when the input is equal to or lower than an
arbitrary low limit.
(State 1) M = 0 @ X ≤ H
(State 2) M = 1 @ X > Η
X
M
X
State State
1
2
L
t
© 2003 by Béla Lipták
t
Output signal type is different from that of input signal.
* is equal to:
E – voltage, A – analog
I – current, B – binary
P – pneumatic, D – digital
R – resistance, H – hydraulic
O – electromagnetic, sonic
t
1.2 Functional Diagrams and Function Symbols
45
TABLE 1.2c Continued
Mathematical Function Block Symbols (proposed for the next revision of ISA S5.1 [now ANSI/ISA-5.01.01] at the time of this writing)
No.
28
Symbol/Function
Equation/Graph
∗HL
Definition
Output states are dependent on value of input.
Output changes state when input is equal to or lower than an
arbitrary low limit or equal to or higher than an arbitrary high limit.
(State 1) M = 1 @ X ≤ L
(State 2) M = 0 @ L < X < H
(State 3) M = 1 @ X ≥ Η
X
High/Low Signal
Monitor
M
X
State
1
H
State
2
State
3
L
t
29
T
t
Output equals input that is selected by transfer.
Transfer is actuated by external signal.
(State 1) M = X1
(State 2) M = X2
X
X1
M
Transfer
State
2
State
1
X2
t
See statement of permission on page 31.
© 2003 by Béla Lipták
t