Parosh Aziz Abdulla Bengt Jonsson On the Existence of Network Invariants for Verifying Parameterized Systems. 180-197 http://link.springer.de/link/service/series/0558/bibs/1710/17100180.htm 1999 conf/birthday/1999langmaack Correct System Design db/conf/birthday/langmaack1999.html#AbdullaJ99