Some countries have integer numbers printed on the transport tickets, for example, in ex-USSR. The ticket is "happy" when the sum of the first half of digits equals to the second one. Then you should eat it and make a wish.
Example:
123456 and 111222 are not happy tickets
123123 and 123222 are the happy tickets
The namespaces conception in C# seems to be exhaustive and insufficient at the same time compared with a strong module notation in Oberon-2 and even with a modular programming approaches in Free Pascal/Delphi.
Why insufficient? You cannot declare constants and functions within namespaces but you should add a class with constant field or static method for it.
Why exhaustive? The using directive with such introduced classes is the source of unexpected errors. Here is an example below.
Example: