Carol E. Cleland

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Propositional reasoning is the ability to draw conclusions on the basis of sentence connectives such as and, if, or, and not. A psychological theory of prepositional reasoning explains the mental operations that underlie this ability. The ANDS (A Natural Deduction System) model, described in the following pages, is one such theory that makes explicit(More)
I explore the conceptual foundations of Alan Turing's analysis of computability, which still dominates thinking about computability today. I argue that Turing's account represents a last vestige of a famous but unsuccessful program in pure mathematics, viz., Hilbert's formalist program. It is my contention that the plausibility of Turing's account as an(More)
Astrobiologists are aware that extraterrestrial life might differ from known life, and considerable thought has been given to possible signatures associated with weird forms of life on other planets. So far, however, very little attention has been paid to the possibility that our own planet might also host communities of weird life. If life arises readily(More)
Since the mid-twentieth century, the concept of the Turing machine has dominated thought about effective procedures. This paper presents an alternative to Turing's analysis; it unifies, refines, and extends my earlier work on this topic. I show that Turing machines cannot live up to their billing as paragons of effective procedure; at best, they may be said(More)
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