Aspects of 3-neutrino mixing and oscillations in vacuum and in matter with constant density are investigated working with a real form of the neutrino Hamiltonian. We find the (approximate) equalities $\theta^m_{23} = \theta_{23}$ and $\delta^m = \delta$, $\theta_{23}$ (...

Comment: 55 pages, 19 figures

Comment: 29 pages, 13 figures, minor text modification consistent with version accepted in PRD