Here is every promise a to-do list makes. VARIABLE tasks Init == tasks = [i \in Ids |-> "absent"] Add(i) == tasks[i] = "absent" /\ tasks' = [tasks EXCEPT ![i] = "open"] Complete(i) == tasks[i] = "open" /\ tasks' = [tasks EXCEPT ![i] = "done"] Reopen(i) == tasks[i] = "done" /\ tasks' = [tasks EXCEPT ![i] = "open"] Delete(i) == tasks[i] # "absent" /\ tasks' = [tasks EXCEPT ![i] = "absent"] ClearCompleted == /\ \E i \in Ids : tasks[i] = "done" /\ tasks' = [i \in Ids |...