Petersonʹs mutual exclusion algorithm revisited

A new derivation of Petersonʹs well-known mutual exclusion algorithm is presented. The derivation is driven by the formally stated requirements of Individual Progress, as opposed to the more traditional approach which starts from the requirement of Mutual Exclusion. The only formalisms used in the derivation are the predicate calculus and the theory of Owicki and Gries. No use is made of temporal logic. In particular, the so complicating oscillating behaviour of an await-condition is fully absorbed by the use of a variant function.