  We analyze a class of positive partial transpose states (PPT) such that the
positivity of its partial transposition is recognized with respect to canonical
factorization of the original density operator (Cholesky block decomposition).
We call such PPT states strong PPT states (SPPT). This property, contrary to
PPT, is basis dependent. It is shown that there exists a proper subset of SPPT
states which are separable and provide a separable decomposition for any of
these states.
