जिंदगी बहुत कुछ सिखाती है ,

कभी हँसाती है तो कभी रुलाती है ,

पर जो हर हाल में खुश रहते हैं ,

जिंदगी उन्ही के आगे सर झुकाती है।

# Lecture - 3 Relations and Functions

**Logic**** for this lecture: **

• Functions \subseteq Relations

• A relation from non-empty set A to non-empty set B is said to be function, if

→ every element of set A has only one image in set B.

In other words, Domain = A and

no distinct ordered pairs have same first element.

**DIFFERENT MAPPINGS OF FUNCTIONS**

**One-One / Injective Mapping / Monomorphism**

A function is said to be one-one if each member of the range of the function arises for one and only one member of the domain of the function.

• A function f: A → B is said to be one-one if f(a) = f(b) \Rightarrow a = b

**Many-One**

A function is said to be many-one if at least one member of the range of the function arises for more than one member of the domain of the function.

• A function f: A → B is said to be one-one if f(a) = f(b) \Rightarrow a \ne b

Onto Mapping / Surjective Function

• In a Surjective function,

Range = Co-domain

Into Mapping

• In a Surjective function,

Range \subset Co-domain

• A function which is both one-one and onto is called Bijective Function.