The post-Christmas rally in stocks resumed last week, after a one-week interruption. The S&P 500 rose 1.6 percent, for its fifth gain in the past six weeks, and has risen 15.1 percent since it hit bottom on Christmas Eve. In the process, the S&P 500 has pushed above the 50-day moving average, after spending a month and a half below it. On Friday, it flirted with the 100-day moving average but ended the day fractionally short. It has been almost four months since the index closed above the 100-day moving average. It remains 7.6 percent below its September peak.