  If alpha=alpha(G) is the maximum size of an independent set and s_{k} equals
the number of stable sets of cardinality k in graph G, then
I(G;x)=s_{0}+s_{1}x+...+s_{alpha}x^{alpha} is the independence polynomial of G.
In this paper we provide an elementary proof of the inequality claiming that
the absolute value of I(G;-1) is not greater than 2^phi(G), for every graph G,
where phi(G) is its decycling number.
