@incollection{JEDP_2000____A10_0,
     author = {Lesch, Matthias},
     title = {Essential self-adjointness of symmetric linear relations associated to first order systems},
     booktitle = {},
     series = {Journ\'ees \'equations aux d\'eriv\'ees partielles},
     eid = {10},
     pages = {1--18},
     publisher = {Universit\'e de Nantes},
     year = {2000},
     mrnumber = {2001m:34184},
     language = {en},
     url = {http://www.numdam.org/item/JEDP_2000____A10_0/}
}