Taylor Swift, Billie Eilish, Lady Gaga, and the Beatles.In a letter Monday to shareholders of his investment fund, Pershing Square, Ackman cited questions from the Securities and Exchange Commission about whether the structure of a special-purpose acquisition company would allow such an acquisition under the rules of the New York Stock Exchange.Vivendi SA last month confirmed that its Universal Music Group was in talks to sell a 10% stake to Pershing's special-purpose acquisition company, or