It is important to understand the origin of exceptional symmetries like E7 duality in 4d M-Sugra. Depending on the context and the defining property at work (anomaly or divergence cancellation, attractor mechanism, classification of supergauge theories in 4, 5 or 6d, 2d integrable systems...) the En groups appear in various families. Cross-fertilization between henceforth parallel problems seems useful.