Welcome to Daveworld

I'd like to take you to an imaginary reality called Daveworld, named after the first person to suffer (imaginary) death therein.

Upon arriving in Daveworld, I first bring a visitor to a large board. On the board is a notice, "You are type..." below which are listed some letters, with a lot of gaps in between. It's as if someone put up a whole alphabet, and then removed most of the letters. Let us imagine that you are type __C____H_JK_____, according to the sign.

Now, for purposes of efficiency, I've brought some other readers along as well, and you can see some of them looking around, having just completed reading the board as well. The conversation that you hear goes as follows:

• Reader 2: "I'm type BCDE? I wonder what that means?"
  
• Reader 3: "I don't know, but it says I'm a type DHI. How about the rest of you?"
  
• Reader 4 seems to not be there, which is too bad, because they were going to lend you an interesting book. Oh well.
  
• Reader 5 says "You're a DEFG? Cool, that's like mine, I'm a EFGH." at the same time as Reader 6 says "DEFG, eh? Well I've got you beat, I'm an ABCD."
  
• Oddly, neither reader 5 nor reader 6 (who are notoriously bad about being gracefully interrupted) seem in the least bit bothered by both talking at once. Readers 2 and 3 also look a bit surprised by this.
  
• There's a bit of a pause, then 5 and 6 both object at the same time, asking what reader 4 means by "please speak one at a time."
  
• 5 also mentions that you, reader 1, are right over where you are, while 6 claims that everyone is there except 5, and doesn't know what 4 is talking about.
  
• 2 and 3 try to reassure everyone that everyone is present, and try to herd 5 and 6 together because obviously something is wrong with their eyes...
  
• And suddenly it seems something is wrong with your eyes, because 5 and 6 end up standing in exactly the same spot... they didn't bump into each other, they just... overlapped. And not only does this seem to not bother them in the least, but they still seem unaware of each other.
  

Such are the confusions that can arise in Daveworld.

If you'd like to puzzle out what's going on, feel free. For everyone else, this may be useful: The big board has, despite appearances, all the letters of the alphabet on it. The board itself is an object of type ABCDEFGHIJKLMNOPetcetera, but each letter is only the type shown on the letter: The letter A is a type A object, the letter Q is a type Q object. In Daveworld, two things can only interact directly if they share a type. The letter Q can stay on the board because both are type Q (among possibly other types). You can see the letters CHJ and K because you are type CHJK, and since you're type C (among other things) you can see the letter C, since you're type J (among other things) you can see the letter J.

In a similar fashion, you share type C with readers 2 and 6, so can hear and see them, type H with reader 3 and 5, but you don't share any types with reader 4 (who's DEFG), so in many regards reader 4 does not exist to you. The same goes for readers 5 and 6, who don't share any types, so don't exist to each other. They can't hear, see, or even bump into the other reader.

For those who are morbidly curious, Dave was a type AB who was a passenger in a type A car driven by a type A person. There was a type BC car driven by a type C driver who couldn't see the type A car or the type AB Dave. Alas, though the BC car would have passed through the A car without damage, it couldn't pass through poor type AB Dave, who in turn could not pass through his type A seat.

The car Dave was riding in spun out of control, what with the passenger seat being forcibly ripped backward due to Dave suddenly exerting a lot of force on it (due to another car exerting a lot of force on him), and the oncoming vehicle got a crumpled front end. While the type A driver and the type C driver survived with substantial injuries and repair bills, Dave was little more than a thin film of liquefied organic matter by the time the cars ground to a halt.

This tale is told to everyone visiting Daveworld in order that they will have an immediate appreciation for the fact that it is not safe to ignore something or someone just because you have non-overlapping types.

It is now time to depart Daveworld, but perhaps we will return another time, if something would be clearer here than in the world we've grown up in.

Incidentally, all the readers you share a type with have assured you that reader 4 wants you to know that, as soon as you're back in the real world, you can borrow that book.