Stocks were narrowly mixed in midday trading Monday as investors sat on the sidelines on the Columbus Day holiday to await a busy earnings week. Twitter (TWTR) was one of the biggest drags, slumping on reports it is set to announce company-wide layoffs this week. Twitter has around 4,200 employees as of last quarter, more than double the number it had when it floated in 2013. Southwest Airlines (LUV) has fixed the computer problems that delayed hundreds of domestic flights over the weekend. System failures had affected its website, apps and airport computers, forcing airport staff to manually process travelers on around 450 flights. Infosys (INFY) fell after reducing its full-year sales forecast due to a stronger U.S. dollar.