BusinessWeek - An investor has capital-gains income from a sold-off stock position. Separately, the investor has other shares that are down an equal amount; if he sold them he'd realize a loss to offset the gains and pay no taxes. But no one likes to sell low. So he wants to use that loss without actually selling the shares. IRS rules prohibit investors from taking a loss against a gain and then buying the shares back within 30 days.
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