Colour-magnitude diagrams of the post-core collapse globular clusters NGC 6256 and NGC 6717 (Palomar 9)S. Ortolani, B. Barbuy and E. BicaAstron. Astrophys. Suppl. Ser., 136 2 (1999) 237-243DOI: https://doi.org/10.1051/aas:1999210