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A fundamental role in our study of actions is played by the situational fluent


Here, p is a person, tex2html_wrap_inline831 is an action or more generally a strategy, and s is a situation. The value of tex2html_wrap_inline835 is the situation that results when p carries out tex2html_wrap_inline831 , starting in the situation s. If the action or strategy does not terminate, tex2html_wrap_inline835 is considered undefined.

With the aid of result we can express certain laws of ability. For example:


This formula is to be regarded as an axiom schema asserting that if in a situation s a person p has a key k that fits the safe sf, then in the situation resulting from his performing the action opens(sf,k), that is, opening the safe sf with the key k, the safe is open. The assertion fits(k,sf) carries the information that k is a key and sf a safe. Later we shall be concerned with combination safes that require p to know the combination.

John McCarthy
Mon Apr 29 19:20:41 PDT 1996