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CSE 20: Discrete Mathematics
Spring 2010
Problem Set 3
Instructor: Daniele Micciancio
Due on:
Thu. April 29, 2010
Problem 1 (25 points)
For each of the following statements,
•
Formulate the statement in the language of prepositional logic. You may use all the standard logic
connectives and quantiﬁers. You may also use the predicate Odd(n) and the relation “ab”. (As a
reminder, the deﬁnition of Odd(n) is
∃
m.n
= 2
m
+ 1
, and the deﬁnition of ab is
∃
c.b
=
ca
.)
•
State if the statement is true or false.
•
Prove your answer correct, i.e., prove either statement or the negation of the statement.
In all statements, the variables range of the set of nonnegative integers.
1. The product of any two odd integers is odd
2. For any two numbers
x
and
y
, the sum
x
+
y
is even if and only if
x
and
y
are either both even or both
odd.
3. For all integers
a,b
and
c
, if
a
divides b and
b
divides
c,
then
a
divides
c
4. The sum of three consecutive integers is always a multiple of 3
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