I argue that it may well be the case that space and time do not consist of points, indeed that they have no smallest parts. I examine two different approaches to such pointless spaces (to 'gunky' spaces): a topological approach and a measure theoretic approach. I argue in favor of the measure theoretic approach.

As McKinsey and Tarksi showed, the Stone representation theorem for Boolean algebras extends to algebras with operators to give topological semantics for (classical) propositional modal logic, in which the "necessity" operation is modeled by taking the interior of an arbitrary subset of a topological space. in this paper the topological interpretation is extended in a natural way to arbitrary theories of full first-order logic. The resulting system of S4 first-order modal logic is complete with respect to such topological semantics.

In the natural sciences higher order structures often occur. There seems to be a need for good methods of describing what we mean by higher order structures in various contexts. This is what hyperstructures are intended to do. We motivate and introduce this new concept. Next we illustrate how it can be applied in various types of genomic analysis—particular the correlations between single nucleotide polymorphisms and diseases. The suggested structure is quite general and may be applied to a variety of (...) situations. Finally we discuss how data sets (f. ex. genomic) may lead to topological spaces, giving new invariants and lead to the prediction of hyperstructures. (shrink)

in Charles Scott and Arleen Dallery, eds., Ethics and Danger: Currents in Continental Thought. Albany. State University of New York Press. 1992. Pp. 83-106.

A first order representation (f.o.r.) in topology is an assignment of finitary relational structures of the same type to topological spaces in such a way that homeomorphic spaces get sent to isomorphic structures. We first define the notions "one f.o.r. is at least as expressive as another relative to a class of spaces" and "one class of spaces is definable in another relative to an f.o.r.", and prove some general statements. Following this we compare some well-known classes of spaces and (...) first order representations. A principal result is that if X and Y are two Tichonov spaces whose posets of zero-sets are elementarily equivalent then their respective rings of bounded continuous real-valued functions satisfy the same positive-universal sentences. The proof of this uses the technique of constructing ultraproducts as direct limits of products in a category theoretic setting. (shrink)

Let M be an o-minimal expansion of an ordered field. Let φ be a formula in the language of ordered domains. In this note we establish some topological properties which are transferred from $\varphi^M$ to $\varphi^R$ and vice versa. Then, we apply these transfer results to give a new proof of a result of M. Edmundo-based on the work of A. Strzebonski-showing the existence of torsion points in any definably compact group defined in an o-minimal expansion of an ordered field.

In this paper we propose an approach to vagueness characterised by two features. The first one is philosophical: we move along a Kantian path emphasizing the knowing subject’s conceptual apparatus. The second one is formal: to face vagueness, and our philosophical view on it, we propose to use topology and formal topology. We show that the Kantian and the topological features joined together allow us an atypical, but promising, way of considering vagueness.

A novel conceptual framework is introduced for the Complexity Levels Theory in a Categorical Ontology of Space and Time. This conceptual and formal construction is intended for ontological studies of Emergent Biosystems, Super-complex Dynamics, Evolution and Human Consciousness. A claim is defended concerning the universal representation of an item’s essence in categorical terms. As an essential example, relational structures of living organisms are well represented by applying the important categorical concept of natural transformations to biomolecular reactions and relational structures that (...) emerge from the latter in living systems. Thus, several relational theories of living systems can be represented by natural transformations of organismic, relational structures. The ascent of man and other living organisms through adaptation, is viewed in novel categorical terms, such as variable biogroupoid representations of evolving species. Such precise but flexible evolutionary concepts will allow the further development of the unifying theme of local-to-global approaches to highly complex systems in order to represent novel patterns of relations that emerge in super- and ultra-complex systems in terms of compositions of local procedures. Solutions to such local-to-global problems in highly complex systems with ‘broken symmetry’ might be possible to be reached with the help of higher homotopy theorems in algebraic topology such as the generalized van Kampen theorems (HHvKT). Categories of many-valued, Łukasiewicz-Moisil (LM) logic algebras provide useful concepts for representing the intrinsic dynamic ‘asymmetry’ of genetic networks in organismic development and evolution, as well as to derive novel results for (non-commutative) Quantum Logics. Furthermore, as recently pointed out by Baianu and Poli (Theory and applications of ontology, vol 1. Springer, Berlin, in press), LM-logic algebras may also provide the appropriate framework for future developments of the ontological theory of levels with its complex/entangled/intertwined ramifications in psychology, sociology and ecology. As shown in the preceding two papers in this issue, a paradigm shift towards non-commutative, or non-Abelian, theories of highly complex dynamics—which is presently unfolding in physics, mathematics, life and cognitive sciences—may be implemented through realizations of higher dimensional algebras in neurosciences and psychology, as well as in human genomics, bioinformatics and interactomics. (shrink)

Must space be a unity? This question, which exercised Aristotle, Descartes and Kant, is a specific instance of a more general one; namely, can the topology of physical space change with time? In this paper we show how the discussion of the unity of space has been altered but survives in contemporary research in theoretical physics. With a pedagogical review of the role played by the Euler characteristic in the mathematics of relativistic spacetimes, we explain how classical general relativity (modulo (...) considerations about energy conditions) allows virtually unrestrained spatial topology change in four dimensions. We also survey the situation in many other dimensions of interest. However, topology change comes with a cost: a famous theorem by Robert Geroch shows that, for many interesting types of such change, transitions of spatial topology imply the existence of closed timelike curves or temporal non-orientability. Ways of living with this theorem and of evading it are discussed. (shrink)

In this article I assess some results that purport to show the existence of a type of 'topological perception', i.e., perceptually based classification of topological features. Striking findings about perception in insects appear to imply that (1) configural, global properties can be considered as primitive perceptual features, and (2) topological features in particular are interesting as they are amenable to formal treatment. I discuss four interrelated questions that bear on any interpretation of findings about the perception of topological properties: what (...) exactly are topological properties, what makes them global , in what sense the quoted findings makes them primitive, and what are the hopes of a formal theory of perception based upon them. I suggest that mathematical topology is not the correct model for cognition topological properties, hence that some other formalism ought to be used—a form of “internalized topology.” However, once the principles of this type of topology are spelled out, they may not be as globalistic as one may have expected. (shrink)

Your left and right hands are now touching each other. This could have been otherwise; but could your hands not be attached to the rest of your body? Sue is now putting the doughnut on the coffe table. She could have left it in the box; but could she have left only the hole in the box? Could her doughnut be holeless? Could it have two holes instead? Could the doughnut have a different hole than the one it has? Some (...) spatial facts seem tainted by necessity. This is problematic, since spatial facts are a paradigm of contingency. But the intermingling of space and modality may be surprisingly intricate. To a degree this is already visible in the part-whole structure of extended bodies. Parthood, itself a prima facie extrinsic relation, has an uncertain modal status. And questions about the necessity or the contingency of spatial facts and relations seem to run parallel to questions about the necessity or the contingency of parthood relations. Consider: Could an object have different parts than the ones it has? Common sense has an easy, affirmative answer to this question. However, 1 there are philosophers who, pressed by the need to overcome difficult conundrums concerning the identity of spatio-temporal particulars, have cast doubts on the adequacy of the common-sense answer. In recent years, for instance, Roderick Chisholm [1973, 1975, 1976] has defended the radical view that a true individual can neither gain nor lose parts, so that each single part is essential to it—a view that has come to be known as mereological es- sentialism. (shrink)

The relationship between q-spaces (c.f. [9]) and quantum spaces (c.f. [5]) is studied, proving that both models coincide in the case of Spec A, the spectrum of a non-commutative C*-algebra A. It is shown that a sober T 1 quantum space is a classical topological space. This difficulty is circumvented through a new definition of point in a quantale. With this new definition, it is proved that Lid A has enough points. A notion of orthogonality in quantum spaces is introduced, (...) which permits us to express the usual topological properties of separation. The notion of stalks of sheaves over quantales is introduced, and some results in categorial model theory are obtained. (shrink)

Possibility and reference have been central topics in metaphysics and the philosophy of language in the past decades. Wolfgang Freitag’s Form and Philosophy provides a novel approach to these notions and their interrelations, based on the concept of form as the key modal concept: form is the possibility space of objects. In its historic dimension, the book analyses the role of form in Ludwig Wittgenstein’s Tractatus Logico-Philosophicus and Immanuel Kant’s Critique of Pure Reason. In its systematic dimension, the book offers (...) an alternative ontological basis to David Armstrong’s combinatorial theory of possibility and rejects David Lewis’ analysis of possibility in terms of possible worlds. Representation is shown to rest on the idea of direct reference as proposed by David Kaplan and Saul Kripke. It is argued that the problem of reference links up with Wittgenstein’s rule-following problem, the nature of which is extensively discussed. It emerges that form and reference are complementary with respect to the notion of representation. Once their individual roles are seen, many metaphysical puzzles appear in a new light or disappear altogether. (shrink)

Elementary submodels of some initial segment of the set-theoretic universe are useful in order to prove certain theorems in general topology as well as in algebra. As an illustration we give proofs of two theorems due to Arkhangelskii concerning cardinal invariants of compact spaces.

This paper will argue that the puzzles about instantaneous velocity, and rates of change more generally, are the result of a failure to recognize an ambiguity in the concept of an instant, and therefore of an instantaneous state. We will conclude that there are two distinct conceptions of a temporal instant: (i) instants conceived as fundamentally distinct zero-duration temporal atoms and (ii) instants conceived as the boundary of, or between,temporally extended durations. Since the concept of classical instantaneous velocity is well- (...) defined only on the second conception of instants, we will conclude that this distinction allows us to avoid the above dilemma. If instantaneous velocity is well-defined then the states of a system at various instants are not logically distinct and thus we cannot generate Zeno’s paradox. However, if we assume that the instants are metaphysically distinct, then instantaneous velocity is not well-defined and thus the second horn of the dilemma about the causal-explanatory role of instantaneous velocity cannot be generated. (shrink)

We extend Moss and Parikh’s bi-modal system for knowledge and effort by means of hybrid logic. In this way, some additional concepts from topology related to knowledge can be captured. We prove the soundness and completeness as well as the decidability of the extended system. Special emphasis will be placed on algebras.

Algebraic/topological descriptions of living processes are indispensable to the understanding of both biological and cognitive functions. This paper presents a fundamental algebraic description of living/cognitive processes and exposes its inherent ambiguity. Since ambiguity is forbidden to computation, no computational description can lend insight to inherently ambiguous processes. The impredicativity of these models is not a flaw, but is, rather, their strength. It enables us to reason with ambiguous mathematical representations of ambiguous natural processes. The noncomputability of these structures means computerized (...) simulacra of them are uninformative of their key properties. This leads to the question of how we should reason about them. That question is answered in this paper by presenting an example of such reasoning, the demonstration of a topological strategy for understanding how the fundamental structure can form itself from within itself. (shrink)

We present and study the category of formal topologies and some of its variants. Two main results are proven. The first is that, for any inductively generated formal cover, there exists a formal topology whose cover extends in the minimal way the given one. This result is obtained by enhancing the method for the inductive generation of the cover relation by adding a coinductive generation of the positivity predicate. Categorically, this result can be rephrased by saying that inductively generated formal (...) topologies are coreflective into inductively generated formal covers. The second result is that unary formal covers are exponentiable in the category of inductively generated formal covers and hence, thanks to the coreflection, unary formal topologies are exponentiable in the category of inductively generated formal topologies. From a localic point of view the exponentiability of unary formal topologies means that algebraic dcpos are exponentiable in the category of open locales. But, the coreflection theorem states that open locales are coreflective in locales and hence, as a consequence of well-known impredicative results on exponentiable locales, it allows to prove that locally compact open locales are exponentiable in the category of open locales. (shrink)

Ted Relph’s review of Heidegger’s Topology acknowledges the importance of Heidegger’s thought in the contemporary turn to place within the Humanities and Social Sciences, just as it acknowledges the importance of the philosophical inquiry into place as such (Relph is also particularly generous in his estimation of the role of my work, in Heidegger’s Topology and elsewhere, in contributing to this). Moreover, Relph provides a strikingly apt and vivid image of the way the concept of ‘place’ has, in recent years, (...) ‘exploded’ across many different areas and disciplines, in a proliferation of different forms and uses. While there are many works that deploy various senses of place, and that also delineate the detailed textures and forms of particular places, when it comes to the theoretical inquiry into place, the focus, for the most part, is not on place as such, but either on the effects of place or else on place as itself an effect of other processes. Thus David Harvey, as Relph notes, treats place as a social construction, claiming that the only interesting question then concerns the social processes that give rise to place (see Harvey, 1996: 293-4) – here place is nothing more than an effect; Doreen Massey, on the other hand, treats place, which she refuses to distinguish from space, as significant largely in terms of the consequences of our imagination of place (see Massey, 2005: esp. 5-8) – here it is the effects of place that are given priority. Even the work of a theorist such as Henri Lefebvre (see especially Lefebvre, 1991), so often cited as a key figure in the literature on place, turns out to be important, less for his elucidation of the concept, than.. (shrink)

This paper explores relationships between many-valued logic and fuzzy topology from the viewpoint of duality theory. We first show a fuzzy topological duality for the algebras of Łukasiewicz n -valued logic with truth constants, which generalizes Stone duality for Boolean algebras to the n -valued case via fuzzy topology. Then, based on this duality, we show a fuzzy topological duality for the algebras of modal Łukasiewicz n -valued logic with truth constants, which generalizes Jónsson-Tarski duality for modal algebras to the (...) n -valued case via fuzzy topology. We emphasize that fuzzy topological spaces naturally arise as spectrums of algebras of many-valued logics. (shrink)

The standard mathematical account of the sub-metrical geometry of a space employs topology, whose foundational concept is the open set. This proves to be an unhappy choice for discrete spaces, and offers no insight into the physical origin of geometrical structure. I outline an alternative, the Theory of Linear Structures, whose foundational concept is the line. Application to Relativistic space-time reveals that the whole geometry of space-time derives from temporal structure. In this sense, instead of spatializing time, Relativity temporalizes space.

Hermann von Helmholtz (1821–1894) participated in two of the most significant developments in physics and in the philosophy of science in the 19th century: the proof that Euclidean geometry does not describe the only possible visualizable and physical space, and the shift from physics based on actions between particles at a distance to the field theory. Helmholtz achieved a staggering number of scientific results, including the formulation of energy conservation, the vortex equations for fluid dynamics, the notion of free energy (...) in thermodynamics, and the invention of the ophthalmoscope. His constant interest in the epistemology of science guarantees his enduring significance for philosophy. (shrink)

We are used to regarding actions and other events, such as Brutus’ stabbing of Caesar or the sinking of the Titanic, as occupying intervals of some underlying linearly ordered temporal dimension. This attitude is so natural and compelling that one is tempted to disregard the obvious difference between time periods and actual happenings in favor of the former: events become mere “intervals cum description”.1 On the other hand, in ordinary circumstances the point of talking about time is to talk about (...) what actually happens or might happen at some time or another. We talk about ‘now’ and ‘then’ in an effort to put some order in our description of what goes on. And since different events seem to overlap in so many different ways, a full account of their temporal relations seems to run afoul of a reductionist strategy. This raises two philosophical questions. The first is whether we can actually go beyond time, as it were, i.e., whether we can take events as bona fide entities and deal with them directly, just as we can deal with spatial entities such as physical bodies or masses without confining ourselves to their spatial representations. This is a controversial issue (though probably not as controversial as it used to be), and ties in with a number of unsettled problems concerning, e.g., the structure of causality or the definition of adequate identity and individuation criteria for events. 2 The second question is whether we can perhaps do without time, i.e., whether we can dispense with time points or intervals as an independent ontological category and focus only on actual or potential happenings, in opposition to the form of reductionism mentioned above—in short, whether we can account for the temporal dimension in terms of suitable relations among events. This is also a highly controversial issue, and relates to the classical dispute concerning relational vs. absolutist conceptions of (space and) time.3 It is this second question that we intend to focus on here.. (shrink)

For the most part, this is a fairly literal translation, but I have opted for a few English idioms for the sake of readability. In that spirit, I have kept the original punctuation, which results in very long sentences, but I have inserted paragraph breaks for readability. I mark these inserted breaks with this sign [¶]; unmarked breaks are in the original. In addition to providing the French for difficult translations, I also interpolate a few English words for readability. Translator’s (...) notes appear as endnotes. (shrink)

For the most part, this is a fairly literal translation, but I have opted for a few English idioms for the sake of readability. In that spirit, I have kept the original punctuation, which results in very long sentences, but I have inserted paragraph breaks for readability. I mark these inserted breaks with this sign [¶]; unmarked breaks are in the original. In addition to providing the French for difficult translations, I also interpolate a few English words for readability. Simondon’s (...) notes appear as footnotes; translator’s notes as endnotes. (shrink)

A topological description of space is given, based on the relation of connection among regions and the property of being limited. A minimal set of 10 constraints is shown to permit definitions of points and of open and closed sets of points and to be characteristic of locally compact T2 spaces. The effect of adding further constraints is investigated, especially those that characterise continua. Finally, the properties of mappings in region-based topology are studied. Not all such mappings correspond to point (...) functions and those that do correspond to continuous functions. (shrink)

He explores what might be called the metaphysics of physics, or maybe just its geometry: as the series title might suggest, topology plays a major role in the ...

The central thesis of this paper is that contemporary theoretical physics is grounded in philosophical presuppositions that make it difficult to effectively address the problems of subject-object interaction and discontinuity inherent to quantum gravity. The core objectivist assumption implicit in relativity theory and quantum mechanics is uncovered and we see that, in string theory, this assumption leads into contradiction. To address this challenge, a new philosophical foundation is proposed based on the phenomenology of Maurice Merleau-Ponty and Martin Heidegger. Then, through (...) the application of qualitative topology and hypernumbers, phenomenological ideas about space, time, and dimension are brought into focus so as to provide specific solutions to the problems of force-field generation and unification. The phenomenological string theory that results speaks to the inconclusiveness of conventional string theory and resolves its core contradiction. (shrink)

As we saw in the Preface, pre-Socratic philosophy viewed nature in the raw as apeiron, the Greek word meaning "limitless," "boundless" or "indeterminate. ...

Recursion or self-reference is a key feature of contemporary research and writing in semiotics. The paper begins by focusing on the role of recursion in poststructuralism. It is suggested that much of what passes for recursion in this field is in fact not recursive all the way down. After the paradoxical meaning of radical recursion is adumbrated, topology is employed to provide some examples. The properties of the Moebius strip prove helpful in bringing out the dialectical nature of radical recursion. (...) The Moebius is employed to explore the recursive interplay of terms that are classically regarded as binary opposites: identity and difference, object and subject, continuity and discontinuity, etc. To realize radical recursion in an even more concrete manner, a higher-dimensional counterpart of the Moebius strip is utilized, namely, the Klein bottle. The presentation concludes by enlisting phenomenological philosopher Maurice Merleau-Ponty’s concept of depth to interpret the Klein bottle’s extra dimension. (shrink)

This essay is written at the crossroads of intuitive holism, as typified in Eastern thought, and the discursive reflectiveness more characteristic of the West. The point of departure is the age-old human need to overcome fragmentation and realize wholeness. Three basic tasks are set forth: to provide some new insight into the underlying obstacle to wholeness, to show what would be necessary for surmounting this blockage, and to take a concrete step in that direction. At the outset, the question of (...) paradox is addressed, examined in relation to Zen meditation, the problem of language, and the thinking of Heidegger. Wholeness is to be realized through paradox, and it is shown that a complete realization requires that paradox be embodied. Drawing from the fields of visual geometry and qualitative mathematics, three concrete models of paradox are offered: the Necker cube, the Moebius surface, and the Klein bottle. In attempting to model wholeness, an important limitation is recognized: a model is a symbolic representation that maintains the division between the reality represented and the act of symbolizing that reality. It is demonstrated that while the first two models are subject to this limitation, the Klein bottle, possessing higher dimensionality, can express wholeness more completely, provided that it is approached in a radically nonclassical way. The final question of this essay concerns its own capability as an essay. It is asked whether the present text is restricted to affording a mere abstract reflection on wholeness, or whether wholeness can tangibly be delivered. (shrink)

PART I. The Moebius Principle in Science and Philosophy INTRODUCTION The papers in part span a seventeen year period (-). The section begins and ends with ...

This paper addresses a central question of contemporary theoretical physics: Can a unified account be provided for the known forces of nature? The issue is brought into focus by considering the recently revived Kaluza-Klein approach to unification, a program entailing dimensional transformation through cosmogony. First it is demonstrated that, in a certain sense, revitalized Kaluza-Klein theory appears to undermine the intuitive foundations of mathematical physics, but that this implicit consequence has been repressed at a substantial cost. A fundamental reformulation of (...) the Kaluza-Klein strategy is then undertaken, one that casts it within a new intuitive context. This is followed by a provisional application of the suggested approach to the specific problem of cosmic evolution. The paper concludes by exploring the far-reaching epistemological implications of the "neo-intuitive" proposal set forth. (shrink)

Let (X, T) be a topological space and *X a nonstandard extension of X. Sets of the form *G, where G ∈ T. form a base for the "standard" topology ST on *X. The topological space (*X, ST ) will be used to study compactifications of (X, T) in a systematic way.

The paper is a contribution to formal ontology. It seeks to use topological means in order to derive ontological laws pertaining to the boundaries and interiors of wholes, to relations of contact and connectedness, to the concepts of surface, point, neighbourhood, and so on. The basis of the theory is mereology, the formal theory of part and whole, a theory which is shown to have a number of advantages, for ontological purposes, over standard treatments of topology in set-theoretic terms. One (...) central goal of the paper is to provide a rigorous formulation of Brentano's thesis to the effect that a boundary can exist as a matter of necessity only as part of a whole of higher dimension which it is the boundary of. It concludes with a brief survey of current applications of mereotopology in areas such as natural-language analysis, geographic information systems, machine vision, naive physics, and database and knowledge engineering. (shrink)

The concept of niche (setting, context, habitat, environment) has been little studied by ontologists, in spite of its wide application in a variety of disciplines from evolutionary biology to economics. What follows is a first formal theory of this concept, a theory of the relations between objects and their niches. The theory builds upon existing work on mereology, topology, and the theory of spatial location as tools of formal ontology. It will be illustrated above all by means of simple biological (...) examples, but the concept of niche should be understood as being, like concepts such as part, boundary, and location, a structural concept that is applicable in principle to a wide range of different domains. (shrink)

By using some classical reasoning we show that any countably presented formal topology, namely, a formal topology with a countable axiom set, is spatial.

In the first part we consider some difficulties that arise as we move from the analysis of spatio- temporal regions to that of their natural occupants, such as physical bodies or events. In the second part we focus on the latter and we give a refined formulation of our argument to the effect that the temporal dimension can be directly construed from a domain of events in terms of the basic mereotopological relations of parthood and boundary.

This paper begins by pointing out that the Aristotelian conception of continuity (synecheia) and the contemporary topological account share the same intuitive, proto-topological basis: the conception of a ?natural whole? or unity without joints or seams. An argument of Aristotle to the effect that what is continuous cannot be constituted of ?indivisibles? (e.g., points) is examined from a topological perspective. From that perspective, the argument fails because Aristotle does not recognize a collective as well as a distributive concept of a (...) multiplicity of points. It is the former concept that allows contemporary topology to identify some point sets with spatial regions (in the proto-topological sense of this term). This identification, in turn, allows contemporary topology to do what Aristotle was unwilling to do: to conceive the property of continuity, as well as the properties of having measure greater than zero and having n- dimension, as emergent properties. Thus, a point set can be continuous (connected) although none of its subsets of sufficiently smaller cardinality can be. Finally, the paper discusses the manner in which a topological principle, viz., the principle that none of the singletons of points of a continuum can be open sets of that continuum, captures certain aspects of the Aristotelian proto-topological conception of the relation between points and continua. E.g., for both Aristotle and contemporary topology, points in a continuum exist simple as limits of the remainder of the continuum: their singletons have empty ?interiors? and, hence, they are not ?chunks? (topologically, regular closed set) of the continuum. (shrink)

We propose a logic for reasoning about metric spaces with the induced topologies. It combines the 'qualitative' interior and closure operators with 'quantitative' operators 'somewhere in the sphere of radius r.' including or excluding the boundary. We supply the logic with both the intended metric space semantics and a natural relational semantics, and show that the latter (i) provides finite partial representations of (in general) infinite metric models and (ii) reduces the standard '∈-definitions' of closure and interior to simple constraints (...) on relations. These features of the relational semantics suggest a finite axiomatisation of the logic and provide means to prove its EXPTIME-completeness (even if the rational numerical parameters are coded in binary). An extension with metric variables satisfying linear rational (in)equalities is proved to be decidable as well. Our logic can be regarded as a 'well-behaved' common denominator of logical systems constructed in temporal, spatial, and similarity-based quantitative and qualitative representation and reasoning. Interpreted on the real line (with its Euclidean metric), it is a natural fragment of decidable temporal logics for specification and verification of real-time systems. On the real plane, it is closely related to quantitative and qualitative formalisms for spatial representation and reasoning, but this time the logic becomes undecidable. (shrink)