Current price $100. Firm puts in order to buy at any price up to $110. The HFC algorithm puts small volume sells to work out that they are doing that, then se

Current price $100. Firm puts in order to buy at any price up to $110. The HFC algorithm puts small volume sells to work out that they are doing that, then sell to them at $109.99. They then turn around and fill their position at any lower prices. If the HFC was not there the limit order would be filled more slowly at lower prices.