Principle of Mathematical Induction
Let P(n) be a property that is defined for integers n, and let a be a fixed integer.
Suppose the following two statements are true:
1. P(a) is true.
2. For all integers k ≥ a, if P(k) is true then P(k + 1) is true.
Then the statement
for all integers n ≥ a, P(n)
is true.