Math 160A - Winter 2016 - Homework #4
Instructor: Sam Buss - UC San Diego
Due Wednesday, February 17, 2016, in class. [Note date change!]
From the textbook.
Section 2.1, pages 79-80: Problem 10.
Section 2.2, pages 99-104: Problems 2, 3, 4, 9.
Problem D. Let A be a set of expressions. Suppose that an effective
procedure M enumerates A as α1 , α2 , α3 , . . . in order of non-decreasing
lengths. That is, for all i ≥ 1, we have |αi+1 | ≥ |αi , where the notation |α|
denotes the length of an expression α. Prove that A is decidable.
Hint: You will need to use different algorithms for the cases where A is
finite and A is infinite.
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