Hi All In the following little example see attachment, I have a problem that in the RunningStateMachine::State2 the on_entry function must be implemented with event1 and with event3 as well but from the logic point of view there is no possibility to call on_entry in RunningStateMachine::State2 with event1. actually at runtime there is no call is happening to to the function : void on_entry(event1 const&,FSM& ) {std::cout << "entering: State2:Event1" << std::endl;} but it must be defined and even implemented ( if no implementation provided linker error occurs). Is it a restriction/bug or I'm missing something ? It is only happening with initial events for substatemachines ? Or is there a kind of pattern to know what events can enter exit a state in a top of the ones present in the transition tables ?. Br. Richie