The priorities of the ALT and PRIALT are under the presence of the PRIPAR not very clear to me. In the following example, the properties of EXAMPLE 1: PAR PAR a! b! ALT a? Pa b? Pb is the same as ALT SKIP PAR b! Pa SKIP PAR a! Pb The ALT selects a guarded process non-deterministically. Under the presence of a PRIPAR things may become more deterministically. In the next example the ALT should *always* choose guard a? in favor of b? so that the highest process (a!) will be served first -- the highest process has a real-time service to full-fill. EXAMPLE 2: PAR PRIPAR a! b! ALT a? Pa b? Pb is the same as PAR b! Pa This property is similar to the following example that uses a PRIALT. EXAMPLE 3: PAR PRIPAR a! b! PRIALT a? Pa b? Pb is the same as PAR b! Pa What will be the properties of the left program when we swap the guards of the PRIALT as shown in the following example? EXAMPLE 4: PAR PRIPAR a! b! PRIALT b? Pb a? Pa Is this example the same as PAR b! Pa or as PAR a! Pb ????? The first is most efficient. Mapping the guards like this may seem silly, but for reusing objects (or processes) that contains a PRIALT somewhere inside this situation can occur easily. For example, in Java we could take an existing process from the shelf and reuse it in a new project. This process could include a PRIALT somewhere in the code and we are unlucky if the priorities of the guards do not match the PRIPAR construction. If the source code is missing (only the class file exists) then we cannot change the order of the guard list -- we are in trouble! If a PRIPAR construct is allowed to overrule the guard priorities then we have a solution. Therefore, it may be convenient that the ALT and PRIALT semantics can adapt themselves to the priority-relations of the surrounding PRIPAR construction. I would say that PAR b! Pa is the same as example 4, but I may be wrong? Suggestions? Gerald.