1. Department of Mathematics, University of Alberta, Edmonton, Alberta, Canada
2. UMR 5208 du CNRS, Institut Camille Jordan, Université Claude Bernard Lyon 1, Villeurbanne, France; and Institute of Mathematics Simion Stoilow of the Romanian Academy, Bucharest, Romania
3. Department of Mathematics, University of Alberta, Edmonton, Alberta, Canada; and Centro de Altos Estudios en Ciencia Exactas, Buenos Aires, Argentina