1. Consider a min-cost network flow problem with extra requirements. For each requirement, either transform it to a standard min-cost network problem, or point out that the requirement is beyond the framework of standard network flow problem. (1) The flow on arc (3,4) cannot be greater than the flow on arc (3,6). (2) The total flow on arcs (3,4) and (3,6) cannot be greater than 10 . (3) The total flow on arcs (3,4) and (3,6) cannot be greater than 10 , and also the total flow on arcs (3,4) and (3,5) cannot be greater than 10 . (4) The flow on arc (7,8) can be more than the arc capacity u78, but the exceeding part of flow is subject a unit cost of 1.5c78. For example, if c78=4,u78=10,x78=15, then the flow cost is 410+1.54(1510)