7-2~?
1. Prove by mathematical induction that 7<sup>n</sup>-2<sup>n</sup> is divisible by 5, for all integers n ?1.
2. For all sets A, B, and C, prove that (A-B)(C-B) = (A?C)-B, using the element
approach.
3. Define (S*)* = S*, where * denotes the Kleene star. Define (S***)* = S***
Is this set bigger than S*? Is it bigger than S?
4. Give a recursive definition for the set of odd integers {1,2,3...}. Can you define the set of
prime numbers using the recursive definition? Explain.
5. Construct a regular expression over the alphabet ? = {a,b} defining a language such that
a) All strings end in a double letter
b) All strings that do not end in a double letter
c) All strings that has abab in it
6. Show that the following pairs of regular expressions over the alphabet ? = {a,b} define the
same language:
a) (ab)a and a(ba)'
b) a(ba+a)'b and aa'b(aa'b)
7. Construct a finite automaton for the following vending machine. The machine accepts
dispenses a candy bar for 30 cents, a bag of chips