Before revision:  In the equilibrium models of investors with heterogeneous beliefs that followed the original work by Harrison and Kreps , investors are risk-neutral, short-selling is prohibited and agents face a constant marginal cost of carrying positions.
After revision:  In the equilibrium models of investors with heterogeneous beliefs that followed the original work by Harrison and Kreps , investors are risk-neutral, short-selling is prohibited and agents face constant marginal costs of carrying positions.