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1. (6 points) Give recursive definitions of each of the following sets. Remember

ID: 3184341 • Letter: 1

Question

1. (6 points) Give recursive definitions of each of the following sets. Remember to include a basis step and a recursive step. Give a brief justification of why your definition works (a) The set of odd integers (both positive and negative) (b) The set of coordinates on the integer grid Z × Z where the sum of the coordinates is even. This erample might help you get started: Let's give a recursive definition of the set of positive multiples of 3. We'll call the set S Basis step: 3ES Recursive step: If x, y are both in S then x+yES The positive multiples of 3 are 3,6,9,12,. We can build each one from earlier ones by adding 3 over and over agam

Explanation / Answer

(a)

Definition of odd integers be defined as

BASE: 1 is an odd integer.

RECURSION: If k is an odd integer, then 2k+1 is an od integer.

Now 1 is an odd integer by the definition base.

with k=1, 2k+1=3, so 3 is an odd inteer.

with k=-1, 2k+1=-1, so -1 is an odd integer.

and so ...,-3,-1,1,3,... are odd integers.

(b)

The grid has a pair of coordinates (x,y)

BASE: x=1, y=1, sum of coordinates x+y=2 is even.

RECURSION: If x=k, y=k, then Sum of coordinates x+y=k+k=2k is even.