Manny Rayner

Using a logic grammar to learn a lexicon

It is suggested that the concept of logic grammar as relation between a string and a parse-tree can be extended by admitting the lexicon as part of the relation. This makes it possible to give a simple and elegant formulation of the process of infering a lexicon from example sentences in conjunction with a grammar. Various problems arising from implementation and complexity factors are considered, and examples are shown to support the claim that the method shows potential as a practical tool for automatic lexicon acquisition.

On the applicability of nonmonotonic logic to formal reasoning in continuous time

The paper criticizes arguments recently advanced by Shoham, McDermott and Sandewall, which purport to demonstrate the relevance of non-monotonic logic to the formalization of reasoning about the evolution of mechanical systems in continuous time. The first half of the paper examines the Extended Prediction Problem of Shoham and McDermott; reasons are given to support the claim that the problem is the product of a mistaken understanding of the the formal basis of Newtonian mechanics, and has no real existence. An example is given showing how, contrary to Shoham and McDermotts arguments, it is possible to formalise reasoning about the evolution of physical systems in continuous time using only classical logic and differential calculus. The second half then reviews Sandewalls non-monotonic logic for almost-continuous systems. Here it is argued that the proposed framework offers only very marginal advantages in compactness of notation, and generally tends to collapse back into classical logic. In summary, I conclude that there is as yet no good reason to believe that non-monotonic logic will be a useful tool in this area.