In a 1959 paper, Pontecorvo listed 21 possible reactions involving neutrinos and noted that some of them could not occur unless the electron neutrino () and the muon neutrino () were one and the same. (Thus an inability to find those reactions would be evidence that there were two types of neutrinos.) This paper introduced this notation for neutrinos, which we use today, and listed the reasons why he felt that having two types of neutrinos was "attractive from the point of view of symmetry and the classification of particles". The prediction that neutrinos associated with electrons are different from those associated with muons was confirmed in 1962. In 1988 Jack Steinberger, Leon M. Lederman and Melvin Schwartz were awarded the Nobel Prize in Physics for the discovery of the muon neutrino.