c:\windows\Microsoft.NET\Framework\v3.5\csc.exe test-792.cs -r:test-792-lib.dll
Microsoft (R) Visual C# 2008 Compiler version 3.5.30729.1
for Microsoft (R) .NET Framework version 3.5
Copyright (C) Microsoft Corporation. All rights reserved.

test-792.cs(9,7): warning CS0612: 'X' is obsolete