Billionaire Carl Icahn has abandoned his effort to encourage Apple to increase its stock repurchasing program, according to a new letter addressed to Apple shareholders. Icahn had aggressively pushed for an increased stock buyback of up to $150 billion, going so far as to recommend a proxy vote for shareholders to support his agenda. In explaining his reversal, Icahn points to a recent decision by Apple to repurchase $14 billion on a dip in the company's stock price following its most recent earnings announcement. Well-known