1. Renata Passos Machado Vieira:
Department of Mathematics, Federal Institute of Education, Science and Technology of the State of Ceara, Brazil
2. Francisco Regis Vieira Alves:
Department of Mathematics, Federal Institute of Education, Science and Technology of the State of Ceara, Brazil
3. Paula Maria
Machado Cruz Catarino:
Department of Mathematics, University of Tras-os-Montes and Alto Douro, Portugal