2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/185217Tri-bimaximal mixing is a specific lepton mixing ansatz, which has been shown to account very successfully for the established neutrino oscillation data. Working in a particular basis (the `circulant basis'), we identify three independent symmetries of tri-bimaximal mixing, which we exploit to set the tri-bimaximal hypothesis in context, alongside some simple, phenomenologically interesting CP-conserving and CP-violating generalisations.10 Pages in LaTeX, No Figures. Version-2 incorporates some minor corrections to referencesHigh Energy Physics - Phenomenologytext