ReutersDavid Einhorn's Greenlight Capital is out with its first quarter letter to investors. The fund delivered 1.3% net of fees in the first quarter, below the S&P 500 index return of 6.1%. Einhorn identified his short position in Tesla as one of the biggest losers in the period. "It was a difficult quarter to be short the bubble basket, and TSLA in particular," he said.