1. Department of Mathematics, University of Évora, 7000-671 Évora, Portugal
2. Center for Research in Mathematics and Applications (CIMA), University of Évora, 7000-671 Évora, Portugal
3. Coordination of Degree in Mathematics, Campus Maceió, Federal Institute of Education, Science and Technology of Alagoas (IFAL), R. Mizael Domingues, 530-Centro, Maceió 57020-600, AL, Brazil