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Avoiding Considering Preconditions

It is a precondition for air travel without additional actions that one be clothed, holds(clothed(traveller),s), that one not be lame tex2html_wrap_inline148 , and tex2html_wrap_inline150 , etc. With a bow towards later explaining how to make this happen using formalized contexts ([McCarthy 1989] (McCarthy 1991,1992) we'll abbreviate the above to the propositional fluents clothed, tex2html_wrap_inline154 and tex2html_wrap_inline156 . In one respect these conditions are similar to the condition that one have a ticket. However, one is willing to specify as part of the formalization of air travel that one have a ticket, but it is not reasonable to refer explicitly to these other conditions.

Here's an approach to doing it. The simplest approach would be to have a fluent ab7(traveller), abbreviated ab7, and have sentences tex2html_wrap_inline162 , etc. We then use tex2html_wrap_inline164 as a precondition for flying. We then circumscribe ab7. This doesn't work well enough for two reasons. First we still have to mention all these other conditions in the circumscription and circumscribe them also. Second, suppose one of the conditions fails, e.g. the traveller is lame so a wheelchair must be provided. Then we lose tex2html_wrap_inline164 , and we haven't got rid of the other conditions.

At present I think the first problem has to be solved by some form of present resembling the scope of [Etherington et al. 1991]. If we circumscribe it, we are jumping to the conclusion that the interfering phenomena aren't present The second problem may perhaps be solved by introducing a parameter exceptions to ab7 and requiring that none of the exceptions be unresolved.

Both of these ideas require details.

John McCarthy
Sat Apr 14 15:17:01 PDT 2001