The set of all possible at_run_time LIVE_TYPEs which are associated with some ownerLIVE_TYPE. There is
exactely one RUN_TIME_SET object for each LIVE_TYPE. The RUN_TIME_SET of a LIVE_TYPE is the set of
possible at_run_time LIVE_TYPEs which can be assigned into a variable of this LIVE_TYPE and which may be
actually held by an expression of the type of owner.
Note: except for some kernel expanded (*), the RUN_TIME_SET of some expanded LIVE_TYPE has only one
element (i.e. the expanded LIVE_TYPE itself).