time: 0
time should be 100 now 
time: 100
setting 'a-' and letting propagate 
expect to see a- in queue 
event queue:
	100	a : 0
time: 105
expect to see b+ in queue 
event queue:
	110	b : 1	[from a:=0]
time: 110
should stop before b executes (still in queue) 
event queue:
	110	b : 1	[from a:=0]
time: 115
'c-' should now be in queue 
event queue:
	120	c : 0	[from b:=1]
time: 120
'c-' should still be in queue 
event queue:
	120	c : 0	[from b:=1]
time: 125
queue is empty now 
event queue:
