21. Mitchell and Stafford [2000] have challenged the magnitude of this long run evidence, but still allow for some underperformance for acquisitions financed by stock. A related debate on whether diversifying acquisitions destroy value has grown too large to survey here. The seminal works are Lang and Stulz [1994] and Berger and Ofek [1995]. Recent work is summarized in Holmstrom and Kaplan [2001] and Stein [2001].