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1
Quantifiers
Supplementary Notes
Prepared by Raymond WongPresented by Raymond Wong
2
e.g.1 (Page 6)
We are going to prove the following claim C is true: statement P(m) is true for each non-negative integer m, namely 0, 1, 2, …
P(0) true
P(1) true
P(2) true
P(3) true
P(4) true
If we can prove that statement P(m) is true for each non-negative integer separately, then we can prove the above claim C is correct.
… true
3
e.g.1
We are going to prove the following claim C is false: statement P(m) is true for each non-negative integer m, namely 0, 1, 2, …
P(0) true
P(1) true
P(2) true
P(3) true
P(4) true
… true
false
There may exist another non-negative integer k such that P(k) is false
4
e.g.1
We are going to prove the following claim C is false: statement P(m) is true for each non-negative integer m, namely 0, 1, 2, …
P(0) false
P(1) false
P(2) true
P(3) true
P(4) true
… true
m2 > m integer 0, 1, 2, …-1, -2,…
02 > 0
12 > 1
22 > 2
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e.g.2 (Page 9)
We are going to prove the following claim C is true: there exists a non-negative integer m such that statement P(m) is true
P(0)
P(1)
P(2) true
P(3)
P(4)
If we can prove that statement P(m) is true for ONE non-negative integer, then we can prove the above claim C is correct.
…
6
e.g.2
We are going to prove the following claim C is false: there exists a non-negative integer m such that statement P(m) is true
If we can prove that statement P(m) is false for each non-negative integer separately, then we can prove the above claim C is false.
P(0) false
P(1) false
P(2) false
P(3) false
P(4) false
… false
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e.g.2
We are going to prove the following claim C is true: there exists a non-negative integer m such that statement P(m) is true
true
22 > 2
P(0)
P(1)
P(2)
P(3)
P(4)
…
m2 > minteger
8
e.g.3 (Page 13)
E.g. Using the quantifier notations, please re-write the Euclid’s division theorem that states
For every positive integer n and every non-negative integer m, there are integers q and r, with 0 r < n such that m = qn + r.
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e.g.3
For every positive integer n and every non-negative integer m, there are integers q and r, with 0 r < n such that m = qn + r.
Since m is non-negativeand n is a positive integer, we derive that q and r are also non-negative.
For every positive integer n and every non-negative integer m, there are non-negative integers q and r, with r < n such that m = qn + r.
Let Z+ be the set of positive integers.
Let N be the set of non-negative integers.
n Z+ ( )m N ( )q N ( )r N ( )(r < n) (m = qn + r)
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e.g.4 (Page 15)
n Z+ ( )m N ( )q N ( )r N ( )(r < n) (m = qn + r)
Let p(m, n, q, r) denote m = nq + r with r < n
n ( )m ( )q ( )r p(m, n, q, r)
If we remove the universe, then we can see the order in which the quantifieroccurs
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e.g.5 (Page 19) Is the following statement true?
x R+ (x > 1)If this statement is correct, we need to prove the following.
P(0) true
P(0.1) true
P(0.2) true
… true
P(1) true
… true
Let P(x) be “x > 1”
12
e.g.5 Is the following statement true?
x R+ (x > 1)If this statement is incorrect, we need to prove the following.
false
P(0)
P(0.1)
P(0.2)
…
P(1)
…
Let P(x) be “x > 1”
13
e.g.5 Is the following statement true?
x R+ (x > 1)If this statement is incorrect, we need to prove the following.
false
P(0)
P(0.1)
P(0.2)
…
P(1)
…
Let P(x) be “x > 1”
Consider x = 0.1
Note that 0.1 R+
“0.1 > 1” is false.
This statement is false.
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e.g.6 (Page 19) Is the following statement true?
x R+ (x > 1)If this statement is correct, we need to prove the following.
Let P(x) be “x > 1”
P(0)
P(0.1)
P(0.2) true
…
P(2)
…
15
e.g.6 Is the following statement true?
x R+ (x > 1)If this statement is incorrect, we need to prove the following.
Let P(x) be “x > 1”
P(0) false
P(0.1) false
P(0.2) false
… false
P(2) false
… false
16
e.g.6 Is the following statement true?
x R+ (x > 1)If this statement is correct, we need to prove the following.
Let P(x) be “x > 1”
P(0)
P(0.1)
P(0.2)
true
…
P(2)
…
Consider x = 2
Note that 2 R+
“2 > 1” is true.
This statement is true.
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e.g.7 (Page 19) Is the following statement true?
x R (y R (y > x))If this statement is correct, we need to prove the following.
Let P(x, y) be “ y > x”
P(0, 0) P(0, 0.1)
P(0, 0.2) true
…
P(0.1, 0) P(0.1, 0.1)
P(0.1, 0.2)
…
true
x = 0
x = 0.1
x = 0.2 true
true
There exists a value y such that P(0, y) is true.
true
There exists a value y such that P(0.1, y) is true.
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e.g.7 (Page 19) Is the following statement true?
x R (y R (y > x))If this statement is incorrect, we need to prove the following.
Let P(x, y) be “ y > x”
P(0, 0) P(0, 0.1)
P(0, 0.2)
…
P(0.1, 0) P(0.1, 0.1)
P(0.1, 0.2)
…
false
x = 0
x = 0.1
x = 0.2
There doest not exist a value y such that P(0.1, y) is true. That is, for each value y R,
P(0.1, y) is false.false
false
false
false
19
e.g.7 Is the following statement true?
x R (y R (y > x))If this statement is correct, we need to prove the following.
Let P(x, y) be “ y > x”
P(0, 0) P(0, 0.1)
P(0, 0.2) true
…
P(0.1, 0) P(0.1, 0.1)
P(0.1, 0.2)
…
true
x = 0
x = 0.1
x = 0.2 true
true
true
Let y = x + 1
Note that, if x R, then y R
“y > x” is true.
This statement is true.
y = 1
y = 1.1
y = 1.2
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e.g.8 (Page 19) Is the following statement true?
x R ( y R (y > x))If this statement is correct, we need to prove the following.
Let P(x, y) be “ y > x”
P(0, 0) P(0, 0.1)
P(0, 0.2) true
…
P(0.1, 0) P(0.1, 0.1)
P(0.1, 0.2)
…
true
x = 0
x = 0.1
x = 0.2 true
true
true
true
true
true
true
true
true
21
e.g.8 Is the following statement true?
x R ( y R (y > x))If this statement is incorrect, we need to prove the following.
Let P(x, y) be “ y > x”
P(0, 0) P(0, 0.1)
P(0, 0.2)
…
P(0.1, 0) P(0.1, 0.1)
P(0.1, 0.2)
…
false
x = 0
x = 0.1
x = 0.2
false
22
e.g.8 Is the following statement true?
x R ( y R (y > x))If this statement is incorrect, we need to prove the following.
Let P(x, y) be “ y > x”
P(0, 0) P(0, 0.1)
P(0, 0.2)
…
P(0.1, 0) P(0.1, 0.1)
P(0.1, 0.2)
…
false
x = 0
x = 0.1
x = 0.2
false
Consider x = 0.1 and y = 0
Note that x R and y R
“y > x” is false.(i.e., “0 > 0.1” is false)
This statement is false.
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e.g.9 (Page 19) Is the following statement true?
x R ((x 0) y R+ (y > x))If this statement is correct, we need to prove the following.
Let P(x, y) be “ y > x”
P(0, 0.1) P(0, 0.2)
P(0, 0.3) true
…
P(0.1, 0.1) P(0.1, 0.2)
P(0.1, 0.3)
…
x = 0
x = 0.1
x = 0.2
true
true
true
true
24
e.g.9 Is the following statement true?
x R ((x 0) y R+ (y > x))If this statement is incorrect, we need to prove the following.
Let P(x, y) be “ y > x”
P(0, 0.1) P(0, 0.2)
P(0, 0.3) false
…
P(0.1, 0.1) P(0.1, 0.2)
P(0.1, 0.3)
…
x = 0
x = 0.1
x = 0.2
false
false
false
false
25
e.g.9 Is the following statement true?
x R ((x 0) y R+ (y > x))
x = 0.2
If this statement is correct, we need to prove the following.
Let P(x, y) be “ y > x”
P(0, 0.1) P(0, 0.2)
P(0, 0.3) true
…
P(0.1, 0.1) P(0.1, 0.2)
P(0.1, 0.3)
…
x = 0
x = 0.1
true
true
true
true
Let x = 0
Note that y R+
(i.e., y > 0)
“y > x” is true.(i.e., “y > 0” is true)
This statement is true.