	0	a : 0
	10	b : 1	[by a:=0]
event queue:
	20	c : 0	[from b:=1]
time: 15
WARNING: pending event for node `c' was overridden.
set c 1 accepted 
event queue:
	15	c : 1
continuing... 
	15	c : 1
now what? 
when does c- get restored, because b is 1? 
since most vacuous events are dropped, c may be stuck... 
'unset' to force a re-evaluation of fanins 
b : 1	[by a:=0]
c : 1
release c by re-evaluation 
event queue:
	25	c : 0
end of queue 
	25	c : 0
event queue:
now empty queue 
