I DON"T KNOW WHERE THE SECOND BRACKET TERM COMES FROM!
Comparing this with the FOC from the development stage, when every firm is a member:
*The agreed valus of <math>s\;</math> (the cost sharing parameter inside the partnership)
We know that <math>\phi=\overline{\phi}\;</math>, but the sign of <math>z^n - z^0\;</math> depends on <math>\rho(c^0)\;</math>, and <math>s^n \;</math> depends on <math>\rho(c^n)\;</math>.
To get <math>\rho\;</math> constant there must be a constant elasticity of demand. There are two possibilities:
*<math>P(X) = \alpha + \beta X ^\gamma\;</math>, which has an elasticity of <math>\epsilon = \gamma - 1\;</math>.
*<math>P(X) = \alpha +\beta \ln X\;</math>, which elasticity of <math>\epsilon = - 1\;</math>.
*Raising <math>\delta\;</math> is increasing the product market competition
*Raising <math>\epsilon\;</math> makes the equilibrium price less responsive to changes in costs
*Raising either <math>\delta\;</math> or <math>\epsilionepsilon\;</math> raises <math>\rho\;</math>, which in turn expands the set of parameters over which industrywide cooperation raises effective R&D.
There are further specific examples in the paper, including Cournot competition.