...

I used the word frame by analogy with the notion of co-ordinate frame in geometry. The geometers of the early part of this century pounded the table about how frames were arbitrary and as much as possible should be done independently of specific frames. In AI there is some choice in deciding what fluents to make primary, but there isn't as much choice as in geometry. The reason is that geometry admits large groups of transformations among equivalent frames. We don't have any use for transformations interchanging locations and colors, although we might have some use for transforming the co-ordinate system used to give locations. Interchanging colors comes up when we consider search heuristics, because it can reduce the number of cases that have to be examined. That's outside the scope of this article.
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...logic.
``Sorted'' is the term used by the logicians. Computer scientists use ``type''. This is a mistake, because the logicians' notion of type is also useful in computer science.
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John McCarthy
Thu Jan 30 13:14:14 PDT 1997