both off 
event queue:
	0	a : 1
	0	b : 0
time: 0
pull with weak 
event queue:
	10	c : 1	[from a:=0]	(weak)
overpower with strong 
WARNING: unstable `c'+
rule: [after 10, weak]	~a:0 -> c+:X
>> cause: `a' (val: 0)
expect unstable overpower 
event queue:
	14	c : 0	[from b:=1]
time: 14
de-assert weak 
time: 14
