I have therefore settled on a program which acts not within the real world, but within a computer, in a ``microworld'' called Eden. Up until the Eighties, much of AI was carried out in such microworlds, working on the principle that if you start small, and simplify a problem to its utmost by working in a simulated environment stripped of all inessentials, you can scale up later to the real world. Thus a lot of research in planning has been done in the blocks world, which consists of a few blocks whose only attributes are colour and size, stacked on a table. In general, such environments are known as microworlds. One of the most famous early AI programs, Shrdlu, was based in a microworld: see, e.g. the account in AI and Natural Man by Boden.