Fanins of node `Z._c':
(from Z):
[after 10]	~a & ~b -> Z._c+
[after 10]	a & b -> Z._c-
[after 10, weak]	~c -> Z._c+
[after 10, weak]	c -> Z._c-
Fanouts of node `Z._c':
(to Z):
[after 10]	Z._c -> c-
[after 10]	~Z._c -> c+
	0	a : 0
	0	b : 0
	10	Z._c : 1	[by b:=0]
	20	c : 0	[by Z._c:=1]
	20	a : 1
	20	b : 1
event queue:
	30	Z._c : 0	[from b:=1]
expect usual instability reported here 
WARNING: unstable `Z._c'-
rule: [after 10]	a:1 & b:0<0><0> -> Z._c-:1
>> cause: `b' (val: 0)
	25	b : 0
