what dll

In TFS, I sometimes need to write a WorkItemChanged event handler. No biggy, plenty of examples on how to do that. But what’s hard to find is what dll is the class Microsoft.TeamFoundation.WorkItemTracking.Server.WorkItemChangedEvent in? In TFS 2008 it was in Microsoft.teamfoundation.WorkitemTracing.Server.WorkItemChangedEvent. In TFS 2010 it is in Microsoft.TeamFoundation.WorkitemTracking.server.DataAccessLayer.Dll.