ist 4 information and logic - paradise.caltech.eduparadise.caltech.edu/ist4/lectures/lect 1114...
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IST 4Information and Logic
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It is all about Algorizmi780-850AD Gottfried Leibniz
1646-1716???
George Booleg1815 –1864
Boolean Proofs: Axioms + Fun
Proof Dependency
A1 A4
Dependency
A1-A4
L1 T1L2 T0
T2
T3
T4
Core Ideain a Proof
A1 A4
in a Proof
A1-A4
L1 T1L2 T0
Core Ideain a Proof
A1 A4
in a Proof
A1-A4
L1 T1L2 T0
P fProofscreating
“simple and correct” simple and correct proofs
How to create“simple and correct” proofs?
lHenri Poincaré Mathematical CreativityHenri Poincaré1854-1912
French mathematician- Topologyp gy- Chaos - Relativity
WooooooW- WooooooW.....- .........
Henri Poincaré1854-1912
What is Mathematical Creation?What is Mathematical Creation?“It does not consist in making new combinations with mathematical entities already known Any one could do mathematical entities already known. Any one could do that...”
vnIeiontn csioiche“To create consists precisely in not making uselesscombinations and in making those which are useful and
vnIeiontn...csioiche
combinations and in making those which are useful and which are only a small minority. Invention is discernment, choice.”
Invention is choice...
Henri Poincaré1854-1912
Start with ignorance...“For fifteen days I strove to prove that there could not be any functions like those I have since called Fuchsian functions. I was then very ignorant; every day I seated myself at myI was then very ignorant; every day I seated myself at mywork table, stayed an hour or two, tried a great number of combinations and reached no results....”
“One evening, contrary to my custom, I drank black coffee d ld l d d f l h
Persistent work... have a break...
and could not sleep. Ideas rose in crowds; I felt them collide until pairs interlocked, so to speak, making a stablecombination..”“...the next morning I had established the existence of a class of Fuchsian functions...”
Henri Poincaré1854-1912
Work... and relax...“Often when one works at a hard question, nothing good is accomplished at the first attack.”p
“Then one takes a rest, longer or shorter, and sits gdown anew to the work.”
““During the first half-hour, as before, nothing is found, and then all of a sudden the decisiveidea presents itself to the mind.”a pr s nts ts f to th m n .
Henri Poincaré1854-1912
Conscious and unconscious“It might be said that the conscious work has been more fruitful because it has been interrupted and the prest has given back to the mind its forceand freshness.”
“But it is more probable that this rest has been
Rest vs unconscious work...But it is more probable that this rest has been
filled out with unconscious work and that the result of this work has afterwards revealed it lf ”itself...”
B l Al bBoolean AlgebraBoolean is not Binary...
Examples of Boolean Algebrasp g
• 0-1 (two valued) Boolean algebra OR / ANDOR / AND
• Arithmetic Boolean algebras moreglcm / gcd
l b f b
more
• Algebra of subsetsunion / intersection
next
• 0-1 vectors next
Algebra of SubsetsAlgebra of Subsets
S is the set of all pointsS is the set of all points
Elements: all possible subsets of a set Sp
+ is union of sets:is intersection of setsis intersection of sets
How many elements? 2|s|
Example: S =
Operations: union and intersection
Elements:
Complement:
Algebra of SubsetsAlgebra of Subsets
Students at Caltech – the “points”Students at Caltech the points
Houses – some of the “elements”
Blacker, Dabney, Fleming, Ricketts 1931
Lloyd, Page, Ruddock
A
1960
1996Avery 1996
An inter-house is a union-houseAn inter house is a union house
S t O tiSet Operationsgraphical representation
Algebra of SubsetsAlgebra of Subsets
Elements: all possible subsets of a set S
+ is union of sets:
Elements: all possible subsets of a set S
+ is union of sets:is intersection of sets:
A AComplement A
Algebra of Subsets: OperationsAlgebra of Subsets Operations
A B
+ is union of sets:
A B
Algebra of Subsets: OperationsAlgebra of Subsets Operations
A B
is intersection of sets:
A B
John Venn 1834 1923
Venn Diagram
1834 - 1923
ACA B ABC
AC
C
B C
A
B C
DD
BCD
ABCD
Construction due to Anthony Edwards, Cambridge U., UK1935-
3
Source: Wikipedia
Construction due to Anthony Edwards, Cambridge U., UK1935-
3
Source: Wikipedia
Construction due to Anthony Edwards, Cambridge U., UK1935-
3
Source: Wikipedia
Construction due to Anthony Edwards, Cambridge U., UK1935-
3
Source: Wikipedia
Construction due to Anthony Edwards, Cambridge U., UK1935-
3
Source: Wikipedia
Construction due to Anthony Edwards, Cambridge U., UK1935-
3
Source: Wikipedia
Construction due to Anthony Edwards, Cambridge U., UK1935-
3
Source: Wikipedia
Construction due to Anthony Edwards, Cambridge U., UK1935-
3
10
2
1
1
0
3
2
2 32
21
Source: Wikipedia
4How many subsets?
24 = 16
0 11,4,6,4,1
11
22
4
1 2
2
3
3 422 33
1 2
Source: WikipediaConstruction due to Edwards
5
55
Source: WikipediaConstruction due to Edwards
6
Source: WikipediaConstruction due to Edwards
6
Source: WikipediaConstruction due to Edwards
6
44
63
1 6 15 20 15 6 1
Source: Wikipedia
1, 6, 15, 20, 15, 6, 1
Construction due to Edwards
What are 0 and 1?
empty set everything
Algebra of Subsets
Elements: all possible subsets of S (there are 2 subsets)|s|Elements all possible subsets of S (there are 2 subsets)
Operations: union and intersection
Example: S =
Operations: union and intersection
Elements:
Complement:
Algebra of SubsetsAlgebra of Subsets
Union
Algebra of SubsetsAlgebra of Subsets
Intersection
Is the Algebra of Subsets Boolean?
YES
??
A = A
A S A
A ASA S = A S
Algebra of SubsetsAlgebra of Subsets
Union
A = A
Algebra of SubsetsAlgebra of Subsets
Intersection
A S = A
Is the Algebra of Subsets Boolean?
YES
??
AA = SA
??
A ASA A =
Is the Algebra of Subsets Boolean?
YES
union and intersectionare commutative
A Bare commutative
Is the Algebra of Subsets Boolean?
YES
A B A BA B
C
A B
C
Is the Algebra of Subsets Boolean?
YES
A B A BA B
C
A B
C
Is the Algebra of Subsets Boolean?
YES
A B A BA B
C
A B
C
Absorption Theoremp
Th 2Theorem 2:
A B
Examples of Boolean Algebrasp g
• 0-1 (two valued) Boolean algebra OR / ANDOR / AND
• Arithmetic Boolean algebras moreglcm / gcd
l b f b
more
• Algebra of subsetsunion / intersection
• 0-1 vectors next
Boolean algebraBoolean algebra0 1 vectors0-1 vectors |s|
S =
Corresponding 0-1 vectors:
(10)(00) (11) (01)
Elements:
Elements are: (00), (11), (10), (01)
01 1100 10
( ), ( ), ( ), ( )
01 1100 10
0000
10
01
11
Union? Bitwise OR
Elements are: (00), (11), (10), (01)
01 1100 10
( ), ( ), ( ), ( )
01 1100 10
00 00 10 01 1100
10
00 10 01 11
10 10 11 11
01 01 1111 01
11 11 111111
Intersection? Bitwise AND
Elements are: (00), (11), (10), (01)
Bitwise AND ( ), ( ), ( ), ( )
01 1100 10 01 1100 10
00 00 00 00 0000
10
00 00 00 00
00 10 00 10
01 00 00 01 01
11 00 10 01 11
Examples of Boolean Algebrasp g
• 0-1 (two valued) Boolean algebra OR / ANDOR / AND
• Arithmetic Boolean algebras moreglcm / gcd
l b f b
more
• Algebra of subsetsunion / intersection
• 0-1 vectors
Boolean algebraBoolean algebraBoolean integersBoolean integers |s|
Bunitskiy Algebra1899
Euclid, 300BCGeorge Boole1815 –1864
1899
Boolean Integers2 x 3 x 5 = 302 x 3 x 7 = 42
Every prime in the prime factorization is a power of one (square-free integer)Elements:
The set of divisors of a Boolean integerThe set of divisors of a Boolean integer
{1,2,3,5,6,10,15,30}
The operations: lcm and gcdThe operations: lcm and gcd
The 0 and 1 elements: 1 and 30
Least Common Multiple
297 = 3x3x3x11 4455 = 3x3x3x3x5x11405 = 3x3x3x3x5
Greatest Common Divisor
297 = 3x3x3x11 27 = 3x3x3405 = 3x3x3x3x5
Euclid, 300BCGeorge Boole1815 –1864 Bunitskiy Algebra
1899
The set of elements: {1,2,3,6}
1899
f { , , , }
The operations: lcm and gcd1 is Boolean 0 6 is Boolean 1
lcm = lowest common multipled d
1 is Boolean 0 6 is Boolean 1
gcd = greatest common divisor
Elements: Set of divisors of an integerElements: Set of divisors of an integer
Is Bunitskiy Algebra a Boolean Algebra?Is Bunitskiy Algebra a Boolean Algebra?YES
6 = 3x2 11
LCM GCD
3 = 3 10 11 01
2 = 2 01Bitwise OR Bitwise AND
1 = 1 00
D
Is Bunitskiy Algebra a Boolean Algebra?Is Bunitskiy Algebra a Boolean Algebra?
30 = 5X3x2 111
YES
30 = 5X3x2
15 = 5X3
111LCM GCD
110
10 = 5X2
6 = 3X2
101
011 111100
6 3X2
100
011
Bitwise OR Bitwise AND5 = 5
D3 = 3
2 = 2
010
0012 = 2
1 = 1
001
000
Two illuminating questions:Two illuminating questions:
1. Why does it work only for Boolean integers?
2. What is the complement?
For which n d s it k?does it work?
6 2 36 = 2 x 3
a and a together must
1 62 3
have all the factors of n
2 33 26 1
a and a can not share factorsneed to be relatively prime6 1 need to be relatively prime
Prime factors appear at most once in n pp
Examples of Boolean Algebrasp gSize 2k They are isomorphic!
• 0-1 (two valued) Boolean algebra OR / ANDOR / AND
• Arithmetic Boolean algebrasglcm / gcd
l b f b• Algebra of subsetsunion / intersection
• 0-1 vectors
Arithmetic Boolean AlgebrasI hi t Al b f S b t Isomorphic to Algebra of Subsets
The set of divisors of a Boolean integerThe set of divisors of a Boolean integer
{1,2,3,6}
The operations: lcm and gcd
The special elements: 1 and 6
Isomorphic to:
Arithmetic / SubsetsArithmetic / Subsets
1 2 3 6lcm
1 1 2 3 6
2 22 6 6
3 63 3 6
6 66 6 6
Arithmetic / SubsetsArithmetic / Subsets
gcd 1 2 3 6
1 1 1 1 1
2 2 21 1
3 3 31 1
6 6321
Boolean algebraBoolean algebraan amazing theoreman amazing theorem
Representation Theorem (Stone 1936):Representation Theorem (Stone 1936):Every finite Boolean algebra is isomorphic to a Booleanalgebra of subsets of some finite set S.
Algebra 1 Algebra 2
elements elements
operations operations
Marshall StoneMarshall Stone
1903-1989
Proved in 1936 90AB = years After BooleyThe Boolean Syntax invented in 1847 has a unique representative semantic!!!M h ll d H d i 1919 Marshall entered Harvard in 1919 intending to continue his studies at Harvard law school; fell in love with
Harlan Fiske Stone12th Ch f J f h
Mathematics, and the rest is history…
12th Chief Justice of the US1941-1946
Marshall had a passion for travel He began Marshall had a passion for travel. He began traveling when he was young and was on a trip to India when he died....
R t ti Th (St 1936)Representation Theorem (Stone 1936):Every finite Boolean algebra is isomorphic to a Booleanl b ith l t b i bit t f fi it l th algebra with elements being bit vectors of finite length
with bitwise operations OR and AND
Two Boolean algebras with m elements are isomorphic
Every Boolean algebra has 2 elementsk
Provides intuition beyond the axioms:We can ‘naturally’ reason about results in Boolean algebra
Every Boolean algebra has 2 elements
We can naturally reason about results in Boolean algebra
Boolean algebraBoolean algebrait is 0 1 it is 0-1... |s|
The 0-1 Theorem
0-1 Theorem:0 1 Theorem:An identity is true for any finite Boolean algebra if and only if it is true for a two valued (0-1)Boolean algebra
Proof: h dProof: The easy direction
Assume an identity true for any finite Boolean algebraAssume an identity true for any finite Boolean algebra
True for 0-1 Boolean algebraTrue for 0 1 Boolean algebra
The 0-1 Theorem
0-1 Theorem:0 1 Theorem:An identity is true for any finite Boolean algebra if and only if it is true for a two valued (0-1)
Proof: h b d
Boolean algebra.
Proof: The non-obvious directionAssume an identity true for a 0-1 Boolean algebraNeed to prove true for any finite Boolean algebra
The key: Stone’s representation theoremy pwlog we can consider bit vectors
Absorption Theoremp
Th 2Theorem 2:
Proof: The identity is true for 0 1 Boolean algebraProof: The identity is true for 0-1 Boolean algebra
0 + 0 0 = 0×0 + 0 1 = 0×1 1 0 11 + 1 0 = 1×1 + 1 1 = 1×
Need to prove it for any Boolean algebra
Example: 0-1 Theoremp
Th 2
By contradiction Assume true for all 0-1 assignmentsand not true for some other assignment
Theorem 2:
Proof (for general algebra):Hence, there must be iti i th bi Proof (for general algebra):
If an identity is not true in general; then there is an assignment of
a position in the binary vector that is violated
g m felements that violates the equality
There exists a 0-1 assignment to the identity that violates the equality, CONTRADICTION!!
Recap: The 0-1 TheorempAn identity is true for any finite Boolean algebra if and only if it is true for a two valued (0-1)Boolean algebra.
Proof: The easy direction• Assume an identity true for any finite Boolean algebra
• 0-1 is a special case: True for 0-1 Boolean algebraThe non-obvious direction• Assume an identity true for a 0-1 Boolean algebra
CONTRADICTION!!
Q• Need to prove true for any finite Boolean algebra• The key: Stone’s representation theorem
A th i t l ‘id tit i l ti ’ i t• Assume there exists a general ‘identity violating’ assignment
• Show that there is a 0-1 ‘identity violating’ assignment
The 0-1 Theorem: Why Only Identities?Why Only Identities?
Cl 0 1 B l l bClaim: Assume 0-1 Boolean algebra
If
Then or
Proof: xy OR(x,y)000110
01110
1111
Q
The 0-1 Theorem: Why Only Identities?Why Only Identities?
Cl b B l l bClaim: Arbitrary Boolean algebra
If
Then or Proof: Claim is NOT TRUE in general!
One week!
3Prove 1 Prove 2
1 2 4
multiply
Need to provide a complete proof
For (c): Sum of products (no need to expand to DNF)