Problem

A function

f

from the set of natural numbers to integers defined by

f(n) = \begin{cases} \frac{n-1}{2}, & \text{when } n \text{ is odd} \\ -\frac{n}{2}, & \text{when } n \text{ is even} \end{cases}

, is (a) One-one but not onto (b) Onto but not one-one (c) One-one and onto both (d) Neither one-one nor onto