1. Give an alternative specification for lighting up a button by using PNs augmented with priorities, instead of timed PNs. Discuss the differences between the two representations. 2. Formalize the first of the two interpretations of the rule on switching the button off that were discussed in our assessment of the informal specification. 3. Formalize the original rule of the informal specifications—that is “in the latter case, if both floor-request buttons are pressed, only one should be canceled?—instead of the pre-sent choice that switches both buttons off.