
# 6: Functions


• 6.1: Introduction to Functions
One of the most important concepts in modern mathematics is that of a function. We often consider a function as some sort of input-output rule that assigns exactly one output to each input. So in this context, a function can be thought of as a procedure for associating with each element of some set, called the domain of the function, exactly one element of another set, called the codomain of the function. This procedure can be considered an input-output-rule.