This paper presents a destributed algorithm that uses weak copy consistency to create mutual exclusion in a distributed computer system. The weak copy consistency is deduced from the uncertainty of state which occurs due to the finite and unpredictable communication delays in a distributed environment. Also the method correlates outdated state information to current state. The average number of messages to enter critical section in the algorithm is n/2 to n messages where n is the number of sites. We show that the algorithm achieves mutual exclusion and the fairness and liveness of the algorithm is proven. We study the performance of the algorithm by simulation technique.

Petri net based satisfiability testing for non-clausal propositional calculus is presented. Every formula in propositional calculus is hierarchically represented by an acyclic free-choice Petri net called logic Petri net. Then a logic Petri net is combined with two way alternating modules, whose number depends upon the number of atoms used in the formula. It is shown that the satisfiability of a formula with non-clausal form can be tested by obtaining reachable firing set of the complete logic Petri net corresponding to the formula under the maximum firing rule.