Relations
Relations - discrete structures used for representing relationships.
Examples of relationships:
Friendship: “x is a friend of y”
Motherhood: “x is the mother of y”
Enrollment: “x is taking y”
Let A and B be sets. A (binary) relation from A to B is a subset of A?B.
E.g. G = {(2,1), (3,1), (4,1), …, (3,2), (4,2), (5,2), …}
If R is a relation, we write xRy for (x,y)?R, and xRy for (x,y)?R.
E.g. Bob F John, 3G1 (or 3ɭ), 1G3 (or 1ɯ), ...
A relation on the set A is a relation from A to A.
E.g. F is a relation on the set of People.