@Paul_Painleve Dispersionless systems are a subject of intense research & have close links to geometry, see e.g. https://t.co/n8tBXOWaAW aka https://t.co/bvkjEmmfLX & https://t.co/0qHHRXxK1L & refs therein, and introductory texts https://t.co/ap2MyQfWgp by El & https://t.co/vucDCjlac8 by Takebe