Four open questions in massive star evolution G. Meynet, P. Eggenberger, S. Ekström, C. Georgy, J. Groh, A. Maeder, H. Saio and T. Moriya EAS Publications Series, 63 (2013) 373-383 Published online: 19 December 2013 DOI: 10.1051/eas/1363042