Megan McArdle: Why AT&T shareholders ought to be worried

A vertical merger is not, as you might suspect, one with an extra-tall stack of paperwork, but an acquisition in which a company buys a supplier or distributor rather than a competitor. Vertical mergers don’t reduce competition the way “horizontal” mergers between competitors do; indeed, it theoretically benefits consumers by reducing costs and streamlining production. Which is why the government has focused its antitrust enforcement on the horizontal variety, and has left vert