Remarks on 2-q-bit states

We distinguish six classes of families of locally equivalent states in a st raightforward scheme for classifying all 2-q-bit states; four of the classe s consist of two subclasses each. The simple criteria that we stated recent ly for checking a given state's positivity and separability are justified, and we discuss some important properties of Lewenstein-Sanpera decompositio ns. An upper bound is conjectured for the sum of the degree of separability of a 2-q-bit state and its concurrence.