Statements Containing Multiple Quantifiers Lecture 11 Section 2.3 Mon, Feb 5, 2007
Multiply Quantified Statements Multiple universal statements x S, y T, P(x, y) y T, x S, P(x, y) The order does not matter. Multiple existential statements x S, y T, P(x, y) y T, x S, P(x, y) The order does not matter.
Mixed Quantifiers Mixed universal and existential statements x S, y T, P(x, y) y T, x S, P(x, y) The order does matter. What is the difference? Compare x R, y R, x + y = 0. y R, x R, x + y = 0.
Mixed Quantifiers Which of the following are true? x R, y R, z R, x(y + z) = 0. x R, y R, z R, x(y + z) = 0. x R, y R, z R, x(y + z) = 0.
Multiply Quantified Statements In the statement x R, y R, z R, x(y + z) = 0. the predicate x(y + z) = 0 must be true for every y and for some x and for some z. However, the choice of x must not depend on y, while the choice of z may depend on y.
Examples Which of the following statements are true? x N, y N, y < x. x Q, y Q, y < x. x R, y R, y < x. x Q, y Q, z Q, x < z < y.
Negation of Multiply Quantified Statements Negate the statement x R, y R, z R, x(y + z) = 0.
Negation of Multiply Quantified Statements Negate the statement x R, y R, z R, x + y + z = 0. ( x R, y R, z R, x + y + z = 0)
Negation of Multiply Quantified Statements Negate the statement x R, y R, z R, x + y + z = 0. ( x R, y R, z R, x + y + z = 0) x R, ( y R, z R, x + y + z = 0)
Negation of Multiply Quantified Statements Negate the statement x R, y R, z R, x + y + z = 0. ( x R, y R, z R, x + y + z = 0) x R, ( y R, z R, x + y + z = 0) x R, y R, ( z R, x + y + z = 0)
Negation of Multiply Quantified Statements Negate the statement x R, y R, z R, x + y + z = 0. ( x R, y R, z R, x + y + z = 0) x R, ( y R, z R, x + y + z = 0) x R, y R, ( z R, x + y + z = 0) x R, y R, z R, (x + y + z = 0)
Negation of Multiply Quantified Statements Negate the statement x R, y R, z R, x + y + z = 0. ( x R, y R, z R, x + y + z = 0) x R, ( y R, z R, x + y + z = 0) x R, y R, ( z R, x + y + z = 0) x R, y R, z R, (x + y + z = 0) x R, y R, z R, x + y + z 0
Negation of Multiply Quantified Statements Consider the statement c R, x R, f(x) = cx has an x-intercept. Its negation is c R, x R, f(x) = cx has no x-intercept. Which statement is true? How would you prove it?
Negation of Multiply Quantified Statements Consider the statement m, b R, x R, f(x) = mx + b has an x-intercept. Its negation is m, b R, x R, f(x) = mx + b has no x-intercept. Which statement is true?
Negation of Multiply Quantified Statements Consider the statement a, b, c R, x R, f(x) = ax 2 + bx + c has an x-intercept. Its negation is a, b, c R, x R, f(x) = ax 2 + bx + c has no x-intercept. Which statement is true?
Negation of Multiply Quantified Statements Consider the statement b, c R, s, t R, x 2 + bx + c = (x – s) 2 + t. Its negation is b, c R, s, t R, x 2 + bx + c (x – s) 2 + t. Which statement is true?