If r = 2, then (G) ≤ a′
2(G) ≤ (G)+1 for every graph G, since a 2-acyclic
edge-coloring coincides with a proper edge-coloring. A 3-acyclic edge-coloring is
also known as an acyclic edge-coloring. The best already known upper bound
for a′
3(G) is due to Ndreca et al. [4], they proved that a′
3(G) ≤ 9.62(G)
for any graph G. In view of the results mentioned above, we can see that
a′
r(G) = O((G)) for r ≤ 3.