led_on -> main_state[label ="back",width=2.5,fixedsize=true, regular=true, shape=circle];
led_off -> main_state[label ="back",width=2.5,fixedsize=true, regular=true, shape=circle];
 main_state -> led_on[label =" toOn",width=2.5,fixedsize=true, regular=true, shape=circle];
 main_state -> led_off[label =" toOff",width=2.5,fixedsize=true, regular=true, shape=circle];
