“…'unsaturated', we must have u i (x) = 0, i.e. u i (x)p i (x) = 0, which means that at the position x, the flow p i (x) has no contribution to the energy function and the flow p i (x), from x ∈ Ω i to the sink t, can be 'cut' off from the energy function of (19). On the other hand, in view of (8), the indicator function u i (x) = 0 definitely means the position x is not labeled as l i .…”