Up to now the aproaches of fault diagnosis at subnetwork-level for anolog circuits using self-testing and mutual-testing are confronted with an essential core problem:Is there an error area when the constrain that all torn nodes are accessible has been broken through?What rule must be followed for the distribution of the accessible nodes?This paper presents a theorem to answer it

and proves that if all torn nodes are accessible it is a special situation of our research for no error area.nexistence.