@ARTICLE\{IMM1983-03680,
    author       = "V. V. Vidal and H. Ravn",
    title        = "The Discrete-Time Maximum Principle - a survey and some new results",
    year         = "1983",
    pages        = "135-152",
    journal      = "International Journal of Control",
    volume       = "40",
    editor       = "",
    number       = "3",
    publisher    = "",
    url          = "http://www2.compute.dtu.dk/pubdb/pubs/3680-full.html"
}