1. National Centre for Advanced Research in Discrete Mathematics, Kalasalingam University, Anand Nagar, Krishnankoil 626126 Tamil Nadu, India,
2. Department of Applied Mathematics and Informatics, Technical University, Letná 9, Košice 04001, Slovakia,
3. Department of Mathematics and Computer Science, Southwestern University, Georgetown TX 78626, U.S.A.,
4. Department of Applied Mathematics and Informatics, Technical University, Letná 9, Košice 04001, Slovakia
5. Department of Mathematics, Faculty of Mathematics and Sciences, Universitas Indonesia, Depok 16424, Indonesia,