Tokamak magnetic field lines described by simple maps - Dedicated to Professor Celso Grebogi on the occasion of his 60th birthdayJ. S.E. Portela, I. L. Caldas and R. L. VianaEur. Phys. J. Special Topics, 165 (2008) 195-210DOI: https://doi.org/10.1140/epjst/e2008-00863-y