Since ARCA and REDI will be combining their order books into one(the ARCA book),i figured ISLD and INCA would do the same.If they do,we hope the matches will be just as fast as ISLD is now.I think after their merger,they might have as much as 40% or so control of Nasdaq volume.In the ideal world,i envision a day when all stocks(listed and nasdaq)will be traded 100% on INCA 24/7,with no short sale rule.