A proper edge-coloring of a graph G is r-acyclic if every cycle C contained
in G is colored with at least min{|C|, r} colors. The r-acyclic chromatic index
of a graph G, denoted by a′
r(G), is the minimum number of colors used in an
r-acyclic edge-coloring. Clearly, a′
r(G) ≥ (G).