Check out chart for details. Summary: wait for price to break through major support then short on re-test. Target the essentially un-tested (tested by three daily candle wicks) previous all-time high breakout area.
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The other thing I was attempting to establish on the chart is price's distance from the 300 simple moving average (blue line). In all of SPX's trading history, there has been few instances of the price trading so far away from it; therefore, I believe it is due for a bit of a pull-back, on that basis alone.