unstable-unknown 
pulling both rails down simultaneously 
WARNING: unstable `f'-
>> cause: `t' (val: 0)
	0	t : 0
instability? 
	0	f : X	[by t:=0]
t : 0
f : X
	0	t : X
pulling one down first (slight time separation) 
	0	t : 0
	5	f : 0
	5	t : X
	5	f : X
pulling one up 
	5	t : 1
	15	f : 0	[by t:=1]
	15	t : 0
	15	t : X
	15	f : X
glitching one up 
	15	t : 1
expect usual instability 
WARNING: unstable `f'-
rule: [after 10]	t:0 -> f-:X
>> cause: `t' (val: 0)
	20	t : 0
