  The main result of this article is the determination of the minimal size for
the general case of problems with two identical patches. This solution is
presented in the explicit form, which allows to recuperate all the cases found
in the literature as particular cases, namely, one isolated fragment, one
single fragment communicating with its neighborhood, a system with two
identical fragments isolated from the matrix but mutually communicating and a
system of two identical fragments inserted in a homogeneous matrix. It is also
addressed the new problem of a single fragment communicating with the matrix,
with different life difficulty of each side. As application, it is found that
the internal condition $a_{0}$ can set which system is the worst to life. This
prediction confirms and extends the prediction already found in the literature
between isolated and non-isolated systems.
