Answering the Sphinx's Questions on Neutrinos
  In answering the difficult questions on neutrinos asked by Sphinx I argue that search for proton decay is the most important experiment in coming 5-10 years. I also emphasize the crucial importance of the neutrinoless double beta decay with sensitivity of <m_{\nu e}> \sim 0.01 eV level as the unique feasible way of directly detecting neutrinos of atmospheric mass scale in laboratories. I point out that, if observed at this level, it means not only that neutrinos are Majorana particle but also that they must obey an inverted mass hierarchy. 
Hisakazu Minakata