1. Department of Education, Federal Institute of Education, Science and Technology of Mato Grosso, Sorriso 78895-150, Brazil
2. Department of Computer Science, Federal Univesity of Juiz de Fora, Juiz de Fora 36036-900, Brazil
3. Department of Computer Science, University of Oxford, Oxford OX3 7LD, UK
4. Departament of Computing, Federal Univesity of Ouro Preto, Ouro Preto 35400-000, Brazil