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**11 - 20**of**20**### My Fourty Years on His Shoulders

, 2008

"... Gödel's legacy is still very much in evidence. His legacy is overwhelmingly decisive, particularly in the arena of general mathematical and philosophical inquiry. The extent of Gödel's impact in the more restricted domain of mathematical practice is more open to question. In fact, there is an in de ..."

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Gödel's legacy is still very much in evidence. His legacy is overwhelmingly decisive, particularly in the arena of general mathematical and philosophical inquiry. The extent of Gödel's impact in the more restricted domain of mathematical practice is more open to question. In fact, there is an in depth assessment of this impact in Macintyre 2009. But even in this comparatively specialized domain, Gödel's impact is seen to be substantial. As indicated here, particularly in section 12, we believe that the potential impact of Gödel's work 2 on mathematical practice is also overwhelming. However, the full realization of this potential impact will have to wait for some new breakthroughs. We have every confidence that these breakthroughs will materialize. Generally speaking, current mathematical practice has now become very far removed from general mathematical and philosophical inquiry, where Gödel's legacy is most decisively overwhelming. However, there are some signs that some of our most distinguished mathematicians recognize the need for some sort of reconciliation. Here is a quote from Atiyah M. 2008b: "Mathematicians took the role of philosophers, but I want to bring the philosophers back in. I hope someday we will be able to explain mathematics in a philosophical way using philosophical methods". We will not attempt to properly discuss the full impact of Gödel's work and all of the ongoing important research programs that it suggests. This would require a book length manuscript. Indeed, there are several books discussing the Gödel legacy from many points of view, including, for example, (Wang 1987, 1996), (Dawson 2005), and the historically comprehensive five volume set (Gödel

### Presentation to the panel, “Does mathematics need new axioms?”

"... The point of departure for this panel is a somewhat controversial paper that I published in the American Mathematical Monthly under the title “Does mathematics need new axioms? ” [4]. The paper itself was based on a lecture that I gave in 1997 to a joint session of the American Mathematical Society ..."

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The point of departure for this panel is a somewhat controversial paper that I published in the American Mathematical Monthly under the title “Does mathematics need new axioms? ” [4]. The paper itself was based on a lecture that I gave in 1997 to a joint session of the American Mathematical Society and the Mathematical Association of America, and it was thus written for a general mathematical audience. Basically, it was intended as an assessment of Gödel’s program for new axioms that he had advanced most prominently in his 1947 paper for the Monthly, entitled “What is Cantor’s continuum problem? ” [7]. My paper aimed to be an assessment of that program in the light of research in mathematical logic in the intervening years, beginning in the 1960s, but especially in more recent years. In my presentation here I shall be following [4] in its main points, though enlarging on some of them. Some passages are even taken almost verbatim from that paper where convenient, though of course all expository background material that was necessary there for a general audience is omitted. 1 For a logical audience I have written before about

### 1. General Remarks. 2. The Completeness Theorem. 3. The First Incompleteness Theorem. 4. The Second Incompleteness Theorem.

, 2006

"... several historical points. 1. GENERAL REMARKS Gödel's legacy is still very much in evidence. His legacy is overwhelmingly decisive, particularly in the arena of general mathematical and2 philosophical inquiry. The extent of Gödel's impact in the more restricted domain of mathematical practice is mor ..."

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several historical points. 1. GENERAL REMARKS Gödel's legacy is still very much in evidence. His legacy is overwhelmingly decisive, particularly in the arena of general mathematical and2 philosophical inquiry. The extent of Gödel's impact in the more restricted domain of mathematical practice is more open to question. In fact, there is an in depth assessment of this impact in Macintyre 2009. But even in this comparatively specialized domain, Gödel's impact is seen to be substantial. As indicated here, particularly in section 12, we believe that the potential impact of Gödel's work on mathematical practice is also overwhelming. However, the full realization of this potential impact will have to wait for some new breakthroughs. We have every confidence that these breakthroughs will materialize. Generally speaking, current mathematical practice has now become very far removed from general mathematical and philosophical inquiry, where Gödel's legacy is most decisively overwhelming. However, there are some signs that some of our most distinguished mathematicians recognize the need for some sort of reconciliation. Here is a quote from Atiyah M. 2008b: "Mathematicians took the role of philosophers, but I want to bring the philosophers back in. I hope someday we will be able to explain mathematics in a philosophical way using philosophical methods".3 We will not attempt to properly discuss the full impact of Gödel's work and all of the ongoing important research programs that it suggests. This would require a book length manuscript. Indeed, there are several books discussing the Gödel legacy from many points of view, including, for example, (Wang 1987, 1996), (Dawson 2005), and the historically comprehensive five volume set (Gödel

### MATHEMATICAL CONCEPTUALISM

"... We must remember that in Hilbert’s time all mathematicians were excited about the foundations of mathematics. Intense controversy centered around the problem of the legitimacy of abstract objects... The contrast with today’s foggy atmosphere of intellectual exhaustion and compartmentalization could ..."

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We must remember that in Hilbert’s time all mathematicians were excited about the foundations of mathematics. Intense controversy centered around the problem of the legitimacy of abstract objects... The contrast with today’s foggy atmosphere of intellectual exhaustion and compartmentalization could not be more striking. — Stephen Simpson ([15], p. 350) From the standpoint of mainstream mathematics, the great foundational debates of the early twentieth century were decisively settled in favor of Cantorian set theory, as formalized in the system ZFC (Zermelo-Fraenkel set theory including the axiom of choice). Although basic foundational questions have never entirely disappeared, it seems fair to say that they have retreated to the periphery of mathematical practice. Sporadic alternative proposals like topos theory or Errett Bishop’s constructivism have never attracted a substantial mainstream following, and Cantor’s universe is generally acknowledged as the arena in which modern mathematics takes place. Despite this history, I believe a strong case can be made for abandoning Cantorian

### MATHEMATICAL CONCEPTUALISM

, 2005

"... We must remember that in Hilbert’s time all mathematicians were excited about the foundations of mathematics. Intense controversy centered around the problem of the legitimacy of abstract objects... The contrast with today’s foggy atmosphere of intellectual exhaustion and compartmentalization could ..."

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We must remember that in Hilbert’s time all mathematicians were excited about the foundations of mathematics. Intense controversy centered around the problem of the legitimacy of abstract objects... The contrast with today’s foggy atmosphere of intellectual exhaustion and compartmentalization could not be more striking. — Stephen Simpson ([14], p. 350) From the standpoint of mainstream mathematics, the great foundational debates of the early twentieth century were decisively settled in favor of Cantorian set theory, as formalized in the system ZFC (Zermelo-Fraenkel set theory including the axiom of choice). Although basic foundational questions have never entirely disappeared, it seems fair to say that they have retreated to the periphery of mathematical practice. Sporadic alternative proposals like topos theory or Errett Bishop’s constructivism have never attracted a substantial mainstream following, and Cantor’s universe is generally acknowledged as the arena in which modern mathematics takes place. Despite this history, I believe a strong case can be made for abandoning Cantorian

### COMPLEXITY CLASSES AS MATHEMATICAL AXIOMS

, 810

"... Abstract. Treating a conjecture, P #P ̸ = NP, on the separation of complexity classes as an axiom, an implication is found in three manifold topology with little obvious connection to complexity theory. This is reminiscent of Harvey Friedman’s work on finitistic interpretations of large cardinal axi ..."

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Abstract. Treating a conjecture, P #P ̸ = NP, on the separation of complexity classes as an axiom, an implication is found in three manifold topology with little obvious connection to complexity theory. This is reminiscent of Harvey Friedman’s work on finitistic interpretations of large cardinal axioms. 1.

### Incompleteness versus a Platonic multiverse

"... The Platonic multiverse view is that there are multiple and incompatible concepts of a set with corresponding Platonic universes. For example the continuum hypothesis may be true in some of these universes and false in others. This philosophical view leads to an approach for exploring mathematics th ..."

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The Platonic multiverse view is that there are multiple and incompatible concepts of a set with corresponding Platonic universes. For example the continuum hypothesis may be true in some of these universes and false in others. This philosophical view leads to an approach for exploring mathematics that is similar to an approach that stems from the more conservative view that infinity is a potential that can never br fully realized. My version of this view sees infinite collections as human conceptual creations that can have a definite meaning even if they cannot exist physically. The integers and recursively enumerable sets are examples. In this view infinite sets are definite things only if they are logically determined by events that could happen in an always finite but potentially infinite universe with recursive laws of physics. This includes much of generalized recursion theory, but can never include absolutely uncountable sets. “Logically determined ” is a philosophical principal that can be partially defined rigorously, but will always be expandable. In this view uncountable sets can be definite

### An overview of the ordinal calculator

"... An ordinal calculator has been developed as an aid for understanding the countable ordinal hierarchy and as a research tool that may eventually help to expand it. A GPL licensed version is available in C++. It is an interactive command line calculator and can be used as a library. It includes notati ..."

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An ordinal calculator has been developed as an aid for understanding the countable ordinal hierarchy and as a research tool that may eventually help to expand it. A GPL licensed version is available in C++. It is an interactive command line calculator and can be used as a library. It includes notations for the ordinals uniquely expressible in Cantor normal form, the Veblen hierarchies and a form of ordinal projection or collapsing using notations for countable admissible ordinals and their limits. The calculator does addition, multiplication and exponentiation on ordinal notations. For a recursive limit ordinal notation, α, it can list an initial segment of an infinite sequence of notations such that the union of the ordinals represented by the sequence is the ordinal represented by α. It can give the relative size of any two notations and it determines a unique notation for every ordinal represented. Input is in plain text. Output can be plain text and/or L ATEX math mode format. This approach is motivated by a philosophy of mathematical truth that sees objectively true mathematics as connected to properties of recursive processes. It suggests that computers are an essential adjunct to human intuition for extending the combinatorially complex parts of objective mathematics.