Sum of exit times in a series of two metastable states Emilio N.M. Cirillo, Francesca R. Nardi and Cristian Spitoni Eur. Phys. J. Special Topics, 226 10 (2017) 2421-2438 Published online: 19 April 2017 DOI: 10.1140/epjst/e2017-70070-6