Is there a platform that can do the following: Stock A Bid 10 Ask 11 Stock B Bid 15 Ask 17 So to buy the pair AB at market Would be (11 - 15) or -4 To sell the pair at market would be (10 - 17) or -7 If I was willing to sell the pair at -6.5. I would like to float one side based on the other side of the other stock. So It would put an order to sell Stock A at 10.50 based on that it could go market on stock B at 17 and get the -6.50 fill. Also it would auto adjust, meaning that if the Ask of stock B lowered to 16.75 it would lower the order of stock A from 10.5 to 10.25. Also being able to incorporate ratio into the equation would be nice.