Cost Sharing and Approximation成本分担与逼近 CostSharingandApproximation成本分担与逼近 Sharingthecost ApproximateCostRecovery:ΣiUpi≥c*(U)usersharescost Competitiveness:ΣiSpi≤c*(S)foranySU:nooverpayment Knownascorein