CS 30: Continuation of
Lecture on Relations
Subtitle
Review
Given sets X and Y:
A relation R is a subset of (or )
The inverse of a relation R is denoted by R-1, which is a subset of Y (or ) such that if xRy
then yR-1x
Review
A function f is a relation

CS 30: Graphs as an
example of a relation
Subtitle
Review
A relation R is a subset of the set .
Example: Let X = cfw_1,2,3,4,5, R = cfw_(1,2), (2,3),(1,4),(5,2),(5,1). R is a relation under
the set X2
This relation can be visualized/represented using a

Counting Techniques SAMPLE PROBLEMS
Important Properties:
A) (rule of sum) If there are n ways to do event A and m ways to do event B, then there are n + m
ways to do event A or B
B) (rule of product) If there are n ways to do event A and m ways to do eve