?url_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.au=Brouwer%2C+F.&rft.aulast=Brouwer&rft.aufirst=F.&rft.issue=5&rft.volume=4&rft.date=1987&rft.issn=0232-9298&rft.atitle=Mixed+qualitative+calculus+and+economic+modeling&rft.title=Systems+Analysis+Modelling+Simulation&rft.pages=399-408&rft.genre=article