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Assume the following code: [ContractClass(typeof(ICC4Contract))] public interface ICC4 { bool IsFooSet { get; } string Foo { get; } } public class CC4 : ICC4 { private string _foo; public bool IsFooSet { get { return Foo != null; } } public string Foo { get { return _foo; } } } [ContractClassFor(typeof(ICC4))] public abstract class ICC4Contract : ICC4 { public bool IsFooSet { get { Contract.Ensures((Contract.Result<bool>() && Foo != null) || !Contract.Result<bool>()); return false; } } public string Foo { get { Contract.Ensures((Contract.Result<string>() != null && IsFooSet) || !IsFooSet); return null; } } } The contracts try to say: IsFooSet will return true if Foo is not null . Foo doesn't return null if IsFooSet returns true . This almost works. However, I get an "ensures unproven" on return _foo; , because the checker doesn't realize that Foo will always equal _foo . Changing Foo to an automatic property with a private setter removes that warning, but I don't want to do that (I don't like automatic properties with private setters). What do I have to change in the above code to make the warning go away while preserving the _foo field? The following doesn't work: Changing IsFooSet to use _foo instead of Foo . It will result in an additional "ensures unproven" on IsFooSet . Adding an invariant Foo == _foo . This will result in an "invariant unproven" on

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