Comparing extended Z with a heterogeneous notation for reasoning about time and space

We contrast using a notation extension with using a combination of notations. Specifically, we compare the use of an extended dialect of Z [10] with a combination of Z and predicative programming notation [6] for algorithm refinement and for reasoning about time and space constraints on systems. We discuss the difficulty of using extended notations versus using heterogeneous notations, and consider when we might prefer to extend or combine notations. We conclude that there exist situations where a heterogeneous notation can be more appropriate to use than an extended notation.