Massive quark production in electron positron annihilation to order K.G. Chetyrkin, A.H. Hoang, J.H. Kühn, M. Steinhauser and T. Teubner Eur. Phys. J. C, 2 1 (1998) 137-150 Published online: 15 March 1998 DOI: 10.1007/s100520050128