Equivalent models with 0 lower bounds can replace models
with lower bounds on flow. Fig. 28 shows a general arc
with the parameters lower bound, upper bound, cost and
gain. An equivalent representation of the arc with zero
lower bounds is also shown. The transformation requires
modification of the external flows at both ends of the
arc. When arcs have equal upper and lower bounds, the
effected arc may be eliminated because its upper bound
on flow will be zero.

Figure 28. Elimination of Lower Bounds