[Solved]Show that this is an equivalence relation

Hi!

I have given av relation **~** by $\displaystyle \mathbb{N}^2$ where:

$\displaystyle (n,m)$ ~ $\displaystyle (k,l) <=> n+l = m+k$

How would you show that **~** is an equivalence relation?

Need something to get me started, though I understand the relation, not just "how" to prove it.

In other words, show that the realtion is reflexive, symmetric and transitive.

Reflexive $\displaystyle a \mathcal{R} a$

Symmetric $\displaystyle a \mathcal{R} b \implies b \mathcal{R} a$

Transative if $\displaystyle a \mathcal{R} b \mbox{ and } b \mathcal{R}c \implies a \mathcal{R}c$

Thanks in advance for any help/tips!