Formula:-

(I) A function is one-one function or an injection if

f(x)=f(y)

⇒ x=y for all x, y ∈ A

or f(x)f(y)

⇒ xy for all x, y ∈ A

(II)if A and B are two non-empty finite sets containing m and n

(i) Number of function from A to B = n^m

(ii) Number of one–one function from A to B

(iii) Number of one-one and onto function from A to B

(iv) Number of onto function from A to B=

F(A)=4 and f(B)=3

Using formula

Number of one–one function from A to B

Number of one-one function from A to B=0