.NET Framework 4.5 is an in-place upgrade for .NET Framework 4.0. What this means is that it's impossible to have both 4.0 and 4.5 installed. If you want to run just a single application on 4.5, you must run all applications written for 4.0 on 4.5 as well. This places some very strong constraints on how compatible such an upgrade must be.

Ever since this was announced, a number of people expressed their concern that the required level of compatibility is not going to be achieved. I'm certainly one of the people who feel an in-place upgrade with so many changes is not such a great idea, to say the least.

Now I'm on 4.5, and I've run into an incompatibility myself. One that makes every single GUI I've built and tested in .NET over the years have a fairly annoying quirk on machines running 4.5. Read on for details.

If you use ILMerge on a WPF project, you might be in for a shock if you add a WPF window to a library used by the project. ILMerge will refuse to proceed with a message looking like this:

    ILMerge.Merge: ERROR!!: Duplicate type
        'XamlGeneratedNamespace.GeneratedInternalTypeHelper'
        found in assembly 'YourAssembly'.

Using a free tool published by my company, it is now possible to work around this problem. Read on for details.

Suppose you are presented with a game. You are given a red and a blue envelope with some money in each. You are allowed to ask an independent party to open both envelopes, and tell you the ratio of blue:red amounts (but not the actual amounts). If you do, the game master replaces the envelopes, and the amounts inside are chosen by him using the same algorithm as before.

You ask the independent observer to check the amounts a million times, and find that half the time the ratio is 2 (blue has twice as much as red), and half the time it's 0.5 (red has twice as much as blue). At this point, the game master discloses that in fact, the way he chooses the amounts mathematically guarantees that these probabilities hold.

Which envelope should you pick to maximize your expected wealth?

It may seem surprising, but with this set-up, the game master can choose to make either red or blue have a higher expected amount of money in it, or make the two the same. Asking the independent party as described above will not help you establish which is which. This is the surprising part and is, in my opinion, the crux of the two envelopes problem.