http://msdn.microsoft.com/en-us/library/bb882516.aspx is concise about the “evolution” of the inline-delegate Technique. Note I call it a “technique” because this is nothing but syntactic sugar. All the different alternative code techniques therein translate to the earliest version. It’s extremely important to know what goes on behind the scene, and that means the earliest, base version.
From the evolution, you can tell that the c# creators intended lambda to be a Wrapper over unicast delegate. In other words, there’s always a unicast delegate instance behind every lambda.
For a bigger picture of delegates, see my post on 2 fundamental categories.