Before revision:  However, we also show that the higher trading frequency  makes markets more fragile, in the following sense : in a high-frequency trading regime, the agents choose to provide liquidity in equilibrium if and only if they are market-neutral (i.e. their beliefs satisfy certain martingale property).
After revision:  On the other hand, the higher trading frequency makes markets more fragile, in the following sense : in a high-frequency trading regime, the agents choose to provide liquidity in equilibrium if and only if they are market-neutral (i.e. their beliefs satisfy certain martingale property).