U.S. regulators have asked Nasdaq OMX Group and NYSE Euronext to come up with a timeline of Thursday's three-hour trading disruption, but the rival exchange operators have been unable to agree on the details, according to several sources familiar with the situation on Monday. Five days after a glitch that paralyzed Nasdaq-listed stocks for three hours on all U.S. markets, Nasdaq and NYSE have a different understanding of what happened in the period preceding and during the blackout, with each side blaming the other for the outage, according to the sources. At the center of the disagreement is the role of Arca, NYSE's fully electronic stock market. The blackout, which saw trading in about 3,200 Nasdaq-listed stocks such as Apple Inc, Google Inc and Facebook Inc grind to a halt, was preceded by connectivity problems between Arca and the Nasdaq-operated Securities Information Processor (SIP). The SIP consolidates stock prices and distributes them to the market. What's not clear is
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