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CSE 311 Foundations of Computing I

Learn the basics of predicate logic, including predicates, quantifiers, and their use in statements. Explore how to relate quantifiers to logical operations and express statements with quantifiers and domains.

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CSE 311 Foundations of Computing I

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  1. CSE 311 Foundations of Computing I Lecture 5 Predicate Logic Spring 2013

  2. Announcements • Reading assignments • Predicates and Quantifiers • 1.4, 1.5 7th Edition • 1.3, 1.4 6thEdition • Hand in Homework 1 now • Homework 2 is available on the website

  3. A B C F F’0 0 0 0 1 0 0 1 1 0 0 1 0 0 1 0 1 1 1 0 1 0 0 0 1 1 0 1 1 0 1 1 0 1 0 1 1 1 1 0 + A’BC + AB’C + ABC’ + ABC A’B’C Highlights from Last LectureSum-of-products canonical form • Also known as Disjunctive Normal Form (DNF) • Also known as minterm expansion F = 001 011 101 110 111 F = F’ = A’B’C’ + A’BC’ + AB’C’

  4. (A’ + B + C) (A + B + C) (A + B’ + C) A B C F F’0 0 0 0 1 0 0 1 1 0 0 1 0 0 1 0 1 1 1 0 1 0 0 0 1 1 0 1 1 0 1 1 0 1 0 1 1 1 1 0 Highlights from Last LectureProduct-of-sums canonical form • Also known as Conjunctive Normal Form (CNF) • Also known as maxterm expansion F = 000 010 100F = F’ = (A + B + C’) (A + B’ + C’) (A’ + B + C’) (A’ + B’ + C) (A’ + B’ + C’)

  5. Highlights from Last LectureS-o-P, P-o-S, and de Morgan’s theorem • Complement of function in sum-of-products form • F’ = A’B’C’ + A’BC’ + AB’C’ • Complement again and apply de Morgan’s and get the product-of-sums form • (F’)’ = (A’B’C’ + A’BC’ + AB’C’)’ • F = (A + B + C) (A + B’ + C) (A’ + B + C) • Complement of function in product-of-sums form • F’ = (A + B + C’) (A + B’ + C’) (A’ + B + C’) (A’ + B’ + C) (A’ + B’ + C’) • Complement again and apply de Morgan’s and get the sum-of-product form • (F’)’ = ( (A + B + C’)(A + B’ + C’)(A’ + B + C’)(A’ + B’ + C)(A’ + B’ + C’) )’ • F = A’B’C + A’BC + AB’C + ABC’ + ABC

  6. Predicate Logic • Predicate or Propositional Function • A function that returns a truth value • “x is a cat” • “x is prime” • “student x has taken course y” • “x > y” • “x + y = z” or Sum(x, y, z) NOTE: We will only use predicates with variables or constants as arguments. Prime(65353)

  7. Quantifiers • x P(x) : P(x) is true for every x in the domain • x P(x) : There is an x in the domain for which P(x) is true Relate  and  to  and 

  8. Statements with quantifiers Domain: Positive Integers • x Even(x) • x Odd(x) • x (Even(x)  Odd(x)) • x (Even(x)  Odd(x)) • x Greater(x+1, x) • x (Even(x)  Prime(x)) Even(x) Odd(x) Prime(x) Greater(x,y) Equal(x,y)

  9. Statements with quantifiers Domain: Positive Integers • xy Greater (y, x) • xy Greater (x, y) • xy (Greater(y, x)  Prime(y)) • x (Prime(x)  (Equal(x, 2)  Odd(x)) • xy(Sum(x, 2, y)  Prime(x)  Prime(y)) Even(x) Odd(x) Prime(x) Greater(x,y) Equal(x,y) Sum(x,y,z)

  10. Statements with quantifiers Domain: Positive Integers Even(x) Odd(x) Prime(x) Greater(x,y) Sum(x,y,z) • “There is an odd prime” • “If x is greater than two, x is not an even prime” • xyz ((Sum(x, y, z)  Odd(x)  Odd(y)) Even(z)) • “There exists an odd integer that is the sum of two primes”

  11. English to Predicate Calculus • “Red cats like tofu” Cat(x) Red(x) LikesTofu(x)

  12. Goldbach’s Conjecture • Every even integer greater than two can be expressed as the sum of two primes Even(x) Odd(x) Prime(x) Greater(x,y) Equal(x,y) • xyz ((Greater(x, 2)  Even(x))  (Equal(x, y+z)  Prime(y)  Prime(z)) Domain: Positive Integers

  13. Scope of Quantifiers • Notlargest(x) y Greater (y, x) z Greater (z, x) • Value doesn’t depend on y or z “bound variables” • Value does depend on x “free variable” • Quantifiers only act on free variables of the formula they quantify •  x ( y (P(x,y)  x Q(y, x)))

  14. Scope of Quantifiers • x (P(x)  Q(x)) vsx P(x) x Q(x)

  15. Nested Quantifiers • Bound variable name doesn’t matter •  x  y P(x, y)  a  b P(a, b) • Positions of quantifiers can change •  x (Q(x)  y P(x, y))  x  y (Q(x)  P(x, y)) • BUT: Order is important...

  16. Quantification with two variables

  17. Negations of Quantifiers • Not every positive integer is prime • Some positive integer is not prime • Prime numbers do not exist • Every positive integer is not prime

  18. De Morgan’s Laws for Quantifiers x P(x) x P(x)  x P(x) x P(x)

  19. De Morgan’s Laws for Quantifiers x P(x) x P(x)  x P(x) x P(x) “There is no largest integer” •   x  y ( x ≥ y) • x  y ( x ≥ y) • x  y  ( x ≥ y) • x  y (y > x) “For every integer there is a larger integer”

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