On the expressive power of Dynamic Logic (Preliminary Report)

We show that “looping” of while-programs can be expressed in Regular First-Order Dynamic Logic, disproving a conjecture made in [Harel-Pratt 1978]. In addition we show that the expressive power of quantifier-free Dynamic Logic increases when nondeterminism is introduced in the programs that are part of formulae of Dynamic Logic. Allowing assignments of random values to variables increases the expressive power even further.