  Started from local universal isotropic disentanglement, a threshold
inequality on reduction factors is proposed, which is necessary and sufficient
for this type of disentanglement processes. Furthermore, we give the conditions
realizing ideal disentanglement processes provided that some information on
quantum states is known. In addition, based on fully entangled fraction, a
concept called inseparability correlation is presented. Some properties on
inseparability correlation coefficient are studied.
