• What is a system?
    Regardless, you are wrong.I like sushi

    Yes, you are right (I am wrong); but then, anything can be proved from an absurd statement.
  • What is a system?
    @Outlander
    Okey-okey, I get your point. But consider this:

    We speak of the solar system.
    We cannot agree on what, exactly, is a system.
    We make the absurd postulate that one planet could be removed from the solar system.
    This could tell us whether the solar system is in fact a system.

    Which clever philosopher stated that from a false (absurd) statement, anything can be proved?
  • What is a system?
    This website has an odd reputation for people "promoting their work" (which, unlike yours, is generally not of high quality) so the site owner, and as a result his staff, tend to frown upon self-promotion in general.Outlander

    I have been warned, quite sternly, about self promoting, but was informed that I may reference my own work. I am trying my level best to adhere to this, quite ambiguous, rule.

    Interesting place, this forum. I ask a simple question about a definition of a system and end up arguing about absurd nonsensical planetary questions. How odd.
  • AI cannot think
    'As of lately a fierce debate has started, even in the public domain, regarding the potential benefits and dangers of artificial intelligence. From our understanding of evolution described in Chapter 3, it is quite easy to understand this debate: Please recollect that there are two attributes of systems that could be used to understand different classes of systems: a classification based on the interaction between a system and a collection of data, and a classification based on the interaction between a system and its purpose. Both these provide an understanding of the evolution of systems. It is my perception that artificial intelligence has progressed quite well in the classes that require interactions with collections of data. It is a very valid and open question if or when artificial intelligence will obtain the capability of abstract thought (Class 7 systems) and even surpass humans.This will not necessarily keep me awake at night, perhaps we humans can learn something from artificial intelligence with this capability. But then, in the worst-case scenario, this might lead to a world war that would surpass any war in the history of Homo sapiens. What most definitely keeps me awake at night is the possibility that artificial intelligence might obtain the capability of survival (Class 3 systems). p117 How I Understand Things. The Logic of Existence.
  • What is a system?
    @Outlander
    Thank you for your kind words and yes the picture in my profile is actually mine. As for the "nice old man" ... that would depend on whom you ask: my grandchildren might agree, might not.

    At the moment I do not have any more pertinent questions for this forum. I will comment on some of the other discussions though. It is difficult to share more of my work: 'If I show you a few pieces of a jigsaw puzzle, they are the only things that you will see - a few pieces of a jigsaw puzzle. I had to build the puzzle to the extent that the picture starts to appear for you to understand the picture that I see.' p232 How I Understand Things. The Logic of Existence

    What exactly is the purpose, extent and method of the Lounge and Shoutbox? Could it help me get a decent, critical, honest review of my work?
  • Information exist as substance-entity?
    Information exists as a configuration of the components of a system. It is implied by the capability of some systems to communicate - to convert data into information and to perceive data depicting information. p47. Thus, the capability of some systems to solicit another system to reconfigure its components implies information. p57. Some configuration of mass or energy that could be perceived, interpreted - or even understood and communicated. p131. How I Understand Things. The Logic of Existence.
  • What is a system?
    Bye! At least I got an answer to my question.
  • What is a system?

    Our solar system is a finely balanced many-body problem, quite difficult to solve mathematically. A two-body problem can be solved analytically but a many-body problem can only be solved numerically. However, please consider the gravitational force exerted on system earth by the following celestial bodies and by system earth on these bodies:

    F(sun) = 3.52E22 newton
    F(moon) = 1.98E20 newton
    F(Neptune) = 2.21E15 newton

    In comparison, the worlds total population exerts a force of 4.86E12 newton on system earth.

    If any of these celestial bodies would be "removed" from the solar system this fine balance would be catastrophically disrupted and the expected environmental disaster would not be a political talking point, it would be de facto. Or if our solar system evolved sans Neptune, our system earth would have evolved completely different to what it did.

    I assume your question was just out of curiosity, or do you want to make a point?
  • What is a system?


    A totally concede that the colloquial use of the word system is ambiguous, hence my question whether philosophy has a definition of a system. A definition that would remove this ambiguity.

    Let me explain with an example: The colloquial use of the word set is just as ambiguous. But in mathematics, therefore also in engineering as well as technology; an ambiguous understanding of set is totally not acceptable. If I may quote the mathematician Charles Wells: "The word or phrase being defined may involve a word that already exists, but the connotations associated with that word are worthless when one undertake to prove something about the concept that the definition defines." or Alexander Backlund: "To bear Systems Theory in mind one should envision some sort of logical and mathematical basis as a formal unambiguous language."

    The ambiguity of a set is removed, for example, with axioms such as those by Zermelo and Fraenkel. It would seem that no such understanding of a system is available.

    I merely enquired whether philosophy has "some sort of logical" definition of a system - philosophers bandy the word around just as most other people. In fact, in 2000, Nicholas Rescher proposed that concepts such as: cohesive systematisation, systemic order, systemic role, system of explanatory understanding, ... just might pay The Price of an Ultimate Theory, but failed to define what he understood with the word system.

    I have asked my question, I have my answer. Thank you for your participation.

    By the way, if Neptune is removed from our solar system, all life on earth will cease to exist - we would not know whether the solar system would still exist or not.
  • What is a system?


    If you read this "thread" carefully you should find that I did not offered any definition of a system. In fact I asked whether philosophy has such a definition:
    I am curious, does philosophy have a definition of a system, or even better, a general systems theory? The word is bandied about ad nauseam and I am not convinced that it is always correctly used!Pieter R van Wyk
    Also, I think I have proved my point: The word system is bandied about ad nauseam without any agreed upon understanding, only some ambiguous notions.

    Then, AI might be a good "sifting filter" but it cannot recognise a valid new contribution to knowledge. Yes, of course, it could tell you whether a certain understanding is in agreement with the understanding of: Aristotle, Jean Baudrillard, Georg Cantor, Charles Darwin, Kurt Godel, Douglas Kellner, Nicholas Reschar, Bertrand Russel, Ernst Zermelo or any other name one could add to this list; or not. Any new knowledge, real, abstract or imaginary is quite beyond its current capability. For these things you will have to use human intelligence.
  • What is a system?


    I believe the answer to this question is not as simple as yes or no. Removing a single part from a system does not necessarily mean it ceases to be a system, although it might. Removing a part may simply change how the system functions. Likewise, adding a part to the system will result in a functional change, or the new part may completely disrupt the system and cause it to collapse or break.

    It seems to me that there exists a minimal construct that represents the simplest form of a particular kind of system. Subtracting any part from this minimal system will destroy it, while adding parts may or may not destroy it, depending of course on the compatibility of the new part with the existing system structure. This essentially allows a system to either evolve or go extinct.

    So i do think your answer to the question is correct, but only in the context of a minimally viable system.
    punos

    Perhaps an interesting argument but, surely, a valid definition of a system must answer the question that is implied by your argument, not so?
  • What is a system?
    If you subtract a part from the system, does it cease to act as a system?apokrisis

    Yes!

    So one could remove any cog in a watch and it would stop telling the time. But if you got a bucket and tried to scoop out every whorl in a turbulent stream, whorls would just keep reappearing until you changed the whole system. Like cutting off the water flow or cooling it until it changed state and became a frozen block of ice.apokrisis

    I understand what you are saying, but I fail to see its relevance to the question.

    You will note this is an easy way to tell mechanical systems and natural systems apart. And so why a mechanical view of nature is felt not to be enough by many philosophers.apokrisis

    You cannot tell me, exactly, what is a system, yet you maintain that your notion (of a system) can distinguish between mechanical systems and natural systems. Then you complain that philosophers finds this insufficient. How odd.

    Topological order tells you that systems form within systems to create a nested hierarchy of order. One kind of thing can become the ground for the next kind of thing. But now your maths and physics has to start getting sophisticated to handle that.apokrisis

    Really, 'systems form within systems', how does this happen? By your definition interactions forms a system (by some unspecified process, I assume), then somehow decide to form a system within a system. How odd.

    The meta-mathematics required to describe a fundamental general system is actually quite simple.

    The Greeks called it a Cosmos. We call it the Universe. Metaphysics would try to understand it as the metalogic of existence.apokrisis

    You did not answer my question. From your definition then: some interactions formed a system of all systems and you call it the Universe. And this Universe is your 'metaphysical extreme'?

    A General Systems Theory such as you have already dismissed. :up:apokrisis

    "Those who say it cannot be done, should not interrupt those who are doing it."
  • What is a system?
    *3. "How I Understand Things: The Logic of Existence"is a book that questions traditional philosophical and logical frameworks to explore how we perceive and understand existence, challenging the notion that logic can fully capture the nature of being. The work critiques classic systems like rationalism and phenomenology, arguing that their separation of mind and body, or their overemphasis on conceptualization, fails to grasp the pervasive reality of existence itself. Instead, it proposes that existence is signified by the verb "to be" within a judgment, rather than residing in the subject or predicate, and invites readers to re-examine their perceptions of knowledge and reality.
    https://www.google.com/search?client=firefox-b-1-d&q=How+I+Understand+Things.+The+Logic+of+Existence
    Gnomon

    I have read this response to my work by an artificial intelligent (AI) agent. One should keep in mind that AI has not obtained the capability of abstract thought as yet. Thus, AI is incapable to understand my work. I am still hoping to find an "astute reader", capable of abstract thought and who subscribe to Leonardo da Vinci's dictum, "Anyone who conducts an argument by appealing to authority is not using his intelligence; he is just using memory."
  • What is a system?


    Apparently, you didn't get a definition that suited your purposes. Perhaps, you should specify a philosophical problem or application to which you want to apply Systems ThinkingGnomon

    My purpose is clearly stated in my question, nothing more, nothing less. And, it would seem, I got me an answer.
  • What is a system?
    Thank you all for your contribution, and the debate that followed from: Does philosophy have a definition of a system? The second question, ... or better, a general systems theory; seemed to be a bit premature for philosophy.

    Since the debate seemed to dry up, allow me to summarise the ten definitions that was mentioned. I will do this in the format; A system is ... that ...

    @Baden a coherency of differences ... differentiate.
    @Gnomon a framework ... possesses properties.
    @T Clark a group of elements ... interact.
    @MoK irreducible entities ... has a set of properties.
    @jgill a set or universe ... explain meaning.
    @apokrisis interactions ... is successful.
    @Astorre elements that interact ... form properties that stabilise.
    @Outlander entities ... recognise with intent of an outcome.
    @punos a set of components ... constitute a whole.
    @Apustimelogist a Markov blanket ... separate a thing from its environment.

    From this I conclude that the answer to my question is NO, only some notions with some similarities. But then, neither does systems- scientist and thinkers have an answer to this question.

    Some follow-up questions, if you are thus inclined:

    From your definition:

    • How do you determine what is part of the system and what is not?
    • Is it possible for a system to contain a system?
    • If yes, what exactly is a system of all systems?
  • What is a system?

    In my experience, there is always someone on the periphery, doggedly trying to describe reality and reconcile all myths and principles into a single systemTom Storm
    Yes, on the face of it, describing reality with a single system does seem to be far fetched, perhaps even absurd. But then, this would depend on one's understanding of reality - an ambiguous notion it would seem - as well as one's understanding of a system - which is exactly the question contemplated by this discussion - also, it would seem, an ambiguous notion.

    Perhaps a better question would be: How do we understand things? Please consider:

    "If and when we consider things, contemplate things and try to understand things, we can consider anything. In doing this we must convert some anything into something. And there are only two ways we can do this: First we could designate some name (perceive some possible purpose) to some collection of anything and then contemplate some valid description of this specific collection. If we can agree on the unique things in this collection we have named, we could have a meaningful conversation about something. This is then the notion of a system, how we understand all physical things, even those physical things that give us a perception and an understanding of abstract things. Let us name this Systems-thinking, for future reference.

    If it is not possible to name something and agree on its constituent parts - we could consider some anything in terms of something else. If we could agree on such a relationship, a meaningful conversation could also ensue. This is how we form an understanding of all conceptual things. And this we could name Relation-thinking for future reference. In both instances some anything is understood as something. p16 How I Understand Things. The Logic of Existence
  • What is a system?
    As a general rule I avoid people who believe they have created system for understanding reality - it's usually the hallmark of a crank and monomaniac.Tom Storm

    Are you saying:

    • that it is impossible to understand this thing we humans named reality?
    • that only cranks and monomaniacs can understand this thing we humans named reality?
  • What is a system?
    In its most general sense, a system can be understood as an organized interconnected set of at least two or more components that collectively constitute a unified whole. The behavior of the whole is conditioned by the interactions of its parts, while the parts, in turn, derive their functions and significance from their relation to the whole. In this respect, a system is indivisible, as the whole cannot exist independently of its parts, nor can the parts operate meaningfully apart from the whole. A genuine system necessarily gives rise to emergent properties, thereby becoming more than merely the sum of its parts.punos

    In my opinion, a spot-on description. Thank you
  • What is a system?


    So a system is all about stabilising instability.apokrisis

    Please, if a system is all about stabilising instability, where does instability come from? Also, is it not true that "instability" is the root cause of innovation, emergence or evolution?
  • What is a system?
    to establish what the "bare bones" definition or criteria for such are, which I believe I have done for you quite nicely.Outlander

    Please, in terms of your "bare bones", is it possible for
    entities or "points"Outlander
    to be a system?
  • What is a system?
    A system is formed of its interactions rather than constructed from its components. So a general systems theory is successful to the degree it takes that idea to its metaphysical extreme.apokrisis

    In my opinion: interactions without components makes no sense at all. Neither does components without interactions. Please, what would entail a "metaphysical extreme"?
  • What is a system?
    A system is a cognitive construct consisting of individual elements that interact dynamically, forming new properties in relation to the individual elements and maintaining stability over time.Astorre

    Thank you for your frank and honest input - this is a good description, one that is generally accepted by the 'systems-thinkers'. But it has a few problems, specifically one that is really a bother to the systems-scientists: How, in general does one determine what is part of a system and what is not. Or in other words, how does one, in general, determine the boundary of a system?
  • What is a system?
    Yes. The modern notion of Systems*1 sometimes gets mired in details.Gnomon

    You answer thus, then, seemingly, concede to my point:
    The word is bandied about ad nauseam and I am not convinced that it is always correctly used!Pieter R van Wyk
  • What is a system?


    This definition looks very similar to one that has been published in 1923 by Lewis, C.I. Facts, Systems and the Unity of the World. The Journal of Philosophy, Vol. 20, No. 6, pp 141 - 151. Apparently without much success.
  • What is a system?
    Systems are coherencies of (self-recreating, in the case of autopoietic systems) differences between themselves and an environmentBaden

    Please explain then, in terms of your definition, how to determine what is part of the system, and what is part of the environment?

    [In general, if posters want non-academic, dumbed-down answers to their questions, why not just ask AI, why ask on a philosophy forum?]Baden

    To my understanding, AI has not achieved the capability of abstract thought (yet) thus asking AI will have no utility - it will only regurgitate. As a really clever guy once said: "Anyone who conducts an argument by appealing to authority is not using his intelligence; he is just using memory." - Leonardo da Vinci (1452 - 1519).
  • What is a system?

    I don't think systems <=> coherencies is any definition.
  • What is a system?

    These "irreducible entities", is that the fundamental particle that the physicist are trying to find?
  • What is a system?

    I agree with your definition, even though I have used some different words. Do you know of any theory that backs up this definition?
  • What is a system?

    Thank you for your contribution - I was hoping for a concise definition backed by a general systems theory. Notions of systems are a dime a dozen
  • What is a system?

    My understanding is that Luhmann worked on social systems, thus not a general systems theory
  • Opening Statement - The Problem
    And, did you discovered a new world? I did!. For example: The emergence of wealth <=> technology predate the emergence of modern Homo sapiens. Thus all human systems is fully embedded in the systems whose purpose is to increase their wealth. That is why the 'human condition' includes strife, civil disobedience, revolution and war.
  • Opening Statement - The Problem

    "You cannot discover new oceans unless you have the courage to lose sight of the shore."
    ... and good luck to you.
  • Opening Statement - The Problem


    Below is a summary of my work, surely you could glean my line of thought from it:

    Chapter 1 - The Problem
    The basic problem is that after 2,600 years of philosophical endeavour we are still suffering from strife, civil disobedience, revolution and war. I introduce the concept of a Geodesic of Knowledge where any point on this geodesic is some assumed truth and the lines are inferences to deduced truths. This geodesic is unnavigable so I define a pole, the Pole of Existence, based on the conditional assumption of the existence of physical things.

    Chapter 2 – Human Perception
    In this chapter I solve the philosophical problem of discernment from two fundamental arguments on existence and understanding. Defining the words: everything, nothing, something, anything, sometime, somewhere, consequential, unique, equivalence, time invariant, perception of data and collections. Collections is defined by ten axioms.

    Chapter 3 – Systems of Things
    A system is defined cognitively and then, with a valid perception of the collections of things and the arguments that make the Zeroth Argument of Understanding valid, the following is mathematically defined: components, interactions and the Laws of Nature, the purpose of a system, duplicate systems and equal systems. Recognising that in general, systems do not come into being in any algebraic manner, they evolve, the fundamental algebra of the properties (mass or energy and information belonging to) of systems is defined. From this, the fundamental and universal boundaries of all systems can be defined. This, however, leads to the Paradox of the Universe: If anything that is something has a purpose (is a system), then everything must have a purpose (be a system). But if everything has a purpose then this purpose is something else than everything. This paradox is resolved.

    Chapter 4 – Evolution of Classes and the Demarcation Meridian
    At least two system attributes could be used to understand different classes of systems: a classification based on the interaction between a system and a collection of data and a classification based on the interaction between a system and its purpose. When the two classifications are combined the following, consequential and subsequential, classes of systems can be identified: The foundational class, a class capable of decision-making, a class that could survive, a class that could communicate, a class that could reason, a class that could create and a class with the capability of abstraction. This classification provides a theory of evolution without any tautologies (a long standing philosophical problem) and solve the demarcation problem (an even longer standing philosophical problem). This classification also provides for a speculation on the fundamental function for systems science.

    Chapter 5 – General Results, a Mathematical Definition, and More Defined Words
    First some results from this understanding, giving evidence that this definition of a system solve a number of problems encountered with current definitions. Then I provide evidence that my definition of a system is, in fact, a mathematical definition. This chapter concludes with some word-definitions based on the definition and understanding of a system: Causality, analysis and synthesis, complexity, technology, economics and jurisprudence, science, engineering, art and war.

    Chapter 6 – Universe-View of Systems
    Using the philosophical notion of a world-view, I give evidence that this theory of systems provides a universe-view of reality. Amongst some other views, it also provides a definitive understanding of the dangers of artificial intelligence.

    Chapter 7 – A Discussion on Salient Results
    A discussion on the cognitive understanding of a system, the systems theory of evolution (defined in chapters 3 and 4), a systems theory of wealth, human phenomena, reality in itself and the reality of abstract systems. This chapter concludes with a speculation on the existence of a God.

    Chapter 8 – Now What?
    A discussion on how this systems theory provides answers to some other philosophical questions: the unreasonable effectiveness of mathematics and whether mathematics was discovered or invented, also a systems perspective on prejudice and how this effects politics and its use of the fallacy of human rights as an entitlement. This chapter concludes with a speculation on what, exactly, is consciousness.

    Chapter 9 – In Defence
    In anticipation to some possible criticisms to this systems theory, I offer four different defences: arguing that this theory is not just plain reductionism, neither incomplete nor inconsistent, a valid systems theory in comparison to a definition proposed by an article published in the IEEE Systems Journal and finally a valid theory of everything – although I would rather name it a Theory of All Human Understanding. I regard two of these defences seminal: the defence that it is neither incomplete nor inconsistent – in contradiction to Gödel’s theorem and that it provides a valid theory of everything – in spite of the philosophical view that such a theory is not possible.

    Chapter 10 – The Answer
    Here I argue that the Geodesic of Understanding and Knowledge, I proposed in my first chapter – my problem statement, is in fact a viable alternative to 2,600 years of philosophical endeavour. It does not provide answers to all problems but it does provide a fundamental structure for a better understanding of life, the Universe and anything.

    Post Scriptum
    Not only do I provide the standard nomenclature, a reference list, and a thesaurus of the words I defined in the text. I also provide a list of 13 projects of enquiry that could be contemplated based on my theory
  • Opening Statement - The Problem
    @Tom Storm & @Gnomon

    I can provide snippets and quotes from my work as much as I like, you will not see the 'full picture' from this quotes, thus you will not understand the picture that I have AND fully described.

    "So, my arguments will not be based on some truth according to: Aristotle, Jean Baudrillard, Georg Cantor, Charles Darwin, Kurt Godel, Douglas Kellner, Nicholas Reschar, Bertrand Russel, Ernst Zermelo or any other name one could add to this list. My arguments are based on the (conditional) truth of the existence of physical things - the valid Pole of Existence (on my Geodesic of Knowledge). It is thus a basic requirement that you, the reader, must also apply your intelligence and not merely your memory." p12 How I Understand Things. The Logic of Existence.

    Thank you for the interest you have shown thus far - I do appreciate it. I have confirmed my problem statement and will conclude with that.
  • Opening Statement - The Problem


    Ervin Laszlo identifies a convergence of crises, including environmental degradation, social instability, and economic challenges, as major world problems. He argues these issues stem from a fragmented, ego-driven worldview and call for a shift towards a holistic, interconnected perspective. Laszlo emphasizes the need for a collective awakening and a move towards unity and compassion to navigate these turbulent timesGnomon

    I have no issue with Ervin Laszlo's problem identification. I've had some communications with the Laszlo family (Erwin and Alexander) - they seem to be working hard on their Upshift Movement, which is just a new religion claiming human 'consciousness' as the latest saviour. The do not seem to be interested in a better understanding of the very foundation on which 'consciousness' is built.
  • Opening Statement - The Problem
    So, right off-the-bat, your Problem Statement is over my head, and above my pay grade . . . . hence "un-navigable. :wink:Gnomon

    Methinks you are short-selling yourself. Moreover, giving up without trying will bring you nowhere.

    So, it seems that you are trying to communicate with philosophical zombies. :joke:Gnomon

    Yes, it would seem that my definition of philosophy is spot-on:

    "Philosophy := The study of questions without answers." p3 How I Understand Things. The Logic of Existence

    What I do find peculiar about this is the apparent disinterest in any utility:

    I'm not sure what philosophy has to do with world peace or orderly behaviour.Tom Storm

    Philosophy is not really equipped to solve the problems you’ve identified.T Clark

    It wasn't philosophers that contributed to our knowledge. It was scientists and inventors of technology.Harry Hindu

    But the philosopher has yet to provide an answer, and many philosophers do not think it possible.Fire Ologist
  • Opening Statement - The Problem


    I have stated, categorically, in my opening statement, that I am not au fait with the 'ism' and 'ology' languages - however, I am pretty convinced that no study of "metaphysical philosophy of materialism" would explain to me why the world is as it is; why we still have poverty and hunger, revolution and war.

    You could consider the veracity of:

    "We humans could argue about the existence of things until the cows come home. The only thing we have is a perception of things, albeit physical, abstract or imaginary things. Through perception, we gain information, glean knowledge, construct abstract things and conjure imaginary things - even play politics." p201 How I Understand Things. The Logic of Existence
  • Opening Statement - The Problem
    Life expectancy has gone up and your book sales have gone down. Is this why philosophy has falied, because you cannot sell your book!?I like sushi

    Your logic is most impressive - a prime example of excellent philosophical reasoning.
  • Opening Statement - The Problem


    No, I do not blame philosophy for all the problems of the world and no, I do not think some "holistic/systems philosophy" will cure any ills of we humans.

    To my knowledge there does not exist any example of communism that has not failed OR is not failing.

    Nowhere AND never, did I claimed to have any solution to the problems of the world. What I do claim is a better understanding of why the world is as it is. An understanding that just might succeed where 2,600 years of philosophy has not succeeded. And, NO, my understanding is NOT based on any philosophy. It is based on the conditional assumption of the existence of physical things, the things that consist of mass OR energy. You can either agree with this logical assumption OR not. If you do agree - my theory is built on this - read on, it might be worth the price. If you do not agree - sit back and watch the future unfold.
  • Opening Statement - The Problem
    In conclusion to this discussion then: Philosophy have no defence against "The only results I see from philosophy are a world in which we are: unable to have peace, unable to eradicate poverty and hunger, and a world in which a well-balanced coexistence with our environment and among ourselves is but a pipe dream."Pieter R van Wyk

    As for the rest of the discussion, I can only give the following "two naive but fundamental logical statements:

    1. Attempting to define or study any ambiguous notion by describing it in terms of other ambiguous words; is inevitably doomed to ambiguity. Adding more and more ambiguous words to this effort will never change this result.
    2. Trying to define or study any ambiguous notion by defining and studying its perceived attributes is a self-referencing exercise. The only possible result of this exercise is that this specific notion ... is this specific notion." p5 How I Understand Things. The Logic of Existence

Pieter R van Wyk

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