Einstein was well-known for his criticism against Copenhagen interpretation of quantum mechanics, and came up with a paradox with his colleagues Podolsky and Rosen to refute it. The first article deals with the paradox. It only assumes “A short introduction to quantum mechanics I: observables and eigenvalues” as prerequisites. “Neutrino oscillation, clarified’’ deals with theoretical background for neutrino oscillation which was already explained at a laymen level in our earlier article “Neutrino oscillation.” Along with that article, basic quantum mechanics and “Relativistic energy” in the section “Theory of Special Relativity and 4-vector” are the prerequisites.