Mathematical induction is a method of proof that involves first proving a statement is true for the base case (usually n=1), and then proving that if the statement holds true for an integer k, it also holds true for k+1. This implies the statement is true for all positive integers n. The well-ordering principle states that any non-empty subset of positive integers that is bounded below, has a least element. Mathematical induction can be used to prove statements involving the positive integers, but not necessarily for rational or real numbers. An example proof using induction demonstrates proving the sum of the first n odd integers equals n^2.