Refresher - Definitions

DEF:

Any well defined list or collection of objects is called a set. The objects comprising the set are called its elements or members.

 

Notation: ${\displaystyle p\in A}$ reads p is a member of A or p belongs to A. ${\displaystyle \left\{\right\}}$ or ${\displaystyle \varnothing }$: Empty or Null set i.e, the set which contains no elements.

DEF: 

If every element of A also belongs to a set B, then A is called a subset of B.

Notation: ${\displaystyle A\subset B}$

DEF: 

All sets are assumed to be a subset of some fixed set called the Universal Set. The Universal set is usually denoted by U or S.