## Functions

Sources:

- Bernard Kolman, Robert C. Busby & Sharon Cutler Ros. (2014). Functions.
*Discrete Mathematical Structures*(6th ed., pp. 206-246). Pearson. - John Hubbard; Barbara Burke Hubbard. (2015).
*Vector calculus, linear algebra, and differential forms: A unified approach*(5th ed., pp. 9-11). Matrix Editions.

In this section we define the notion of a function, a special type of *relation*.