RDP 2009-03: Competition Between Payment Systems: Results Equation (C6)

f_{j}^{c, +} \equiv f_{j}^{c, *} + \frac{κ}{M} (\frac{D_{i}^{m}}{D_{i}^{m} D_{j}^{m} - D_{i}^{m} D_{i, j; i}^{m} - D_{j}^{m} D_{i, j; j}^{m}}) .