Node a attributes:
Node b attributes:
Node c attributes: ignore_interference
	0	a : 1
	0	b : 1
	10	c : 0	[by b:=1]
now interfere! 
should have no diagnostic 
	10	a : 0
	20	c : X	[by a:=0]
remove interference... 
	20	a : 1
	30	c : 0	[by a:=1]
now weak interference... 
WARNING: weak-interference `c'
>> cause: `a' (val: X)
	30	a : X
	40	c : X	[by a:=X]
remove interference... 
	40	a : 1
	50	c : 0	[by a:=1]
flip side... 
	50	b : 0
	50	a : 0
	60	c : 1	[by a:=0]
interfere pull-down 
but message should be suppressed... 
	60	b : 1
	70	c : X	[by b:=1]
remove interference... 
	70	b : 0
	80	c : 1	[by b:=0]
now weak interference... 
WARNING: weak-interference `c'
>> cause: `b' (val: X)
	80	b : X
	90	c : X	[by b:=X]
remove interference... 
	90	b : 0
	100	c : 1	[by b:=0]
both off... 
	100	a : 1
X-pull-up 
	100	a : X
	100	a : 1
X-pull-down 
	100	b : X
	110	c : X	[by b:=X]
	110	b : 0
X vs. X 
	110	a : X
WARNING: weak-interference `c'
>> cause: `b' (val: X)
	110	b : X
more weak interference... 
WARNING: weak-interference `c'
>> cause: `a' (val: 0)
	110	a : 0
WARNING: weak-interference `c'
>> cause: `a' (val: X)
	110	a : X
more weak interference... 
WARNING: weak-interference `c'
>> cause: `b' (val: 1)
	110	b : 1
WARNING: weak-interference `c'
>> cause: `b' (val: X)
	110	b : X
