Abstract
We consider some advanced topics in logic including fuzzy logic, temporal logic, intuitionist logic, undefined values in logic, logic and AI and theorem provers. Fuzzy logic is an extension of classical logic that acts as a mathematical model for vagueness. Temporal logic is concerned with the expression of properties that have time dependencies. Brouwer and others developed intuitionist logic as the logical foundation for intuitionism, which was a controversial theory of the foundations of mathematics based on a rejection of the law of the excluded middle and an insistence on constructive existence. We discuss several approaches that have been applied to dealing with undefined values that arise with partial functions including the logic of partial functions; Dijkstra’s approach with his cand and cor operators; and Parnas’s approach which preserves a classical two-valued logic.
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Notes
- 1.
It is best to avoid undefinedness by taking care with the definitions of terms and expressions.
- 2.
The above expression would evaluate to true under Jones three-valued logic of partial functions.
- 3.
The above expression evaluates to true for Parnas logic (a two-valued logic).
- 4.
It seems strange to assign the value false to the primitive predicate calculus expression y = 1/0.
- 5.
The approach avoids the undefined logical value (⊥) and preserves the two-valued logic.
- 6.
First-order logic allows quantification over objects but not functions or relations. Higher-order logics allow quantification of functions and relations.
- 7.
For example, the statement ∃x such that x = √4 states that there is an x such that x is the square root of 4, and the constructive existence yields that the answer is that x = 2 or x = −2 i.e. constructive existence provides more the truth of the statement of existence, and an actual object satisfying the existence criteria is explicitly produced.
- 8.
John McCarthy received the Turing Award in 1971 for his contributions to Artificial Intelligence. He also developed the programming language LISP.
- 9.
Perhaps a good analogy might be that a mathematical proof is like a program written in a high-level language such as C, whereas a formal proof in logic is like a program written in assembly language.
- 10.
Russell is said to have remarked that he was delighted to see that the Principia Mathematica could be done by machine and that if he and Whitehead had known this in advance that they would not have wasted 10 years doing this work by hand in the early twentieth century.
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O’Regan, G. (2017). Advanced Topics in Logic. In: Concise Guide to Formal Methods. Undergraduate Topics in Computer Science. Springer, Cham. https://doi.org/10.1007/978-3-319-64021-1_7
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