In user manual :
Starting with CLR v4, the contract class and related types are located in mscorlib.dll. Prior to CLR v4, these types appear in a separate assembly called Microsoft. Contracts dll, which is installed under% ProgramFiles% / Microsoft / Contracts / PublicAssemblies. You may need to add a link to this assembly if you are compiling against version 4.0 of the CLR.
You may have interesting problems if you want to use the same built-in assembly against 3.5 and 4.0 (I don’t know - it can work), but if you just use 3.5, this should be good.
The extension installs in VS2008 as well as VS2010, I suppose.
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