@other{https://resolver.caltech.edu/CaltechTHESIS:03212013-111445922,
    title = "Invariants, Lie-Bäcklund operators and Bäcklund transformations",
    year = "1979",
    url = "https://resolver.caltech.edu/CaltechTHESIS:03212013-111445922",
    id = "record",
    doi = "10.7907/A8EZ-HA03"
}