Which of the following are true statements regarding Arbitrage?

Select one or more:

a. Applying the Ross APT model in search of investment opportunities contains an inherent contradiction

b. Albeit popular, arbitrage theory is but one of many equilibrium concepts that can be used to find prices

c. Risk Arbitrage is not truly Arbitrage from the perspective of a Pure Arbitrage ardent (believer)

d. Pure Arbitrage is a theoretical construct

e. Risk Arbitrage never accounts for the frictions in the market

f. Neither Risk nor Pure Arbitrage can be used practically in pricing securities