(These are the market notes on today's action by Mike Santoli, CNBC's Senior Markets Commentator. See today's video update from Mike above.) A firm but noncommittal start to the week, the indexes continuing to hover just below record highs on selected mega-cap strength and constant rotation. Nvidia , after a few days of shallow downside chop, had a sturdy bid and accounts for most of the S & P 500 's slim quarter-percent gain. Energy , last week's comeback player, was off 2% on a supply-driven slide in crude prices. The so-called "dispersion trade" has been quite active since the traditionally weak seasonal stretch began in August. This features stocks moving their own way, mechanical shifts in flows among sectors, suppressing index-level volatility and keeping the market in equilibrium as

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