WASHINGTON (AP) — The head of publishing titan Penguin Random House on Thursday defended his company’s deal to acquire rival Simon & Schuster against the government’s claim it would thwart competition. But he acknowledged that the merger would buttress his company’s position as the biggest U.S. publisher by expanding its market share. Under questioning at a federal antitrust trial, CEO Markus Dohle also admitted that while he has promised to allow the two merged companies to continue to bid against each other for deals with authors, Penguin Random House’s German parent firm has no legal obligation to honor that commitment.