# Showing a function defined on the integers is continuous

1. Nov 26, 2012

### mbloch10

1. The problem statement, all variables and given/known data

Suppose that the function f is defined only on the integers. Explain why it is continuous.

2. Relevant equations

The ε/δ definition of continuity at a point c:
for all ε > 0, there exists a δ > 0 such that |f(x) - f(c)| ≤ ε whenever |x - c| ≤ δ

3. The attempt at a solution

I understand this completely when we are defining our function on ℝ. I can't intuitively understand this for the integers. I am thinking that if we choose δ = 1, that somehow guarantees that |f(x) - f(c)| will be small enough, but I'm not sure of this because my intuition is stuck in the reals.

2. Nov 26, 2012

### Michael Redei

You'd be better off with any δ<1, even δ=0.9 or δ=0.99999 will do. Imagine a drawing of the real line with the integers marked. Draw a circle around any integer c with radius δ. Since δ isn't quite 1, this circle wihh not quite reach c+1 on the one side or c-1 on the other. So the only integer x within this circle is x=c. And |f(x) - f(c)| = |f(c) - f(c)| is smaller than any ε>0.