A coinductive approach to verified exact real number computation

We present an approach to verified programs for exact real number computation that is based on inductive and coinductive definitions and program extraction from proofs. We informally discuss the theoretical background of this method and give examples of extracted programs implementing the translation between the representation by fast converging rational Cauchy sequences and the signed binary digit representations of real numbers

From Verified Models to Verifiable Code

Declarative specifications of digital systems often contain parts that can be automatically translated into executable code. Automated code generation may reduce or eliminate the kinds of errors typically introduced through manual code writing. For this approach to be effective, the generated code should be reasonably efficient and, more importantly, verifiable. This paper presents a prototype code generator for the Prototype Verification System (PVS) that translates a subset of PVS functional specifications into an intermediate language and subsequently to multiple target programming languages. Several case studies are presented to illustrate the tool's functionality. The generated code can be analyzed by software verification tools such as verification condition generators, static analyzers, and software model-checkers to increase the confidence that the generated code is correct

Encoding of Predicate Subtyping with Proof Irrelevance in the ??-Calculus Modulo Theory

The ??-calculus modulo theory is a logical framework in which various logics and type systems can be encoded, thus helping the cross-verification and interoperability of proof systems based on those logics and type systems. In this paper, we show how to encode predicate subtyping and proof irrelevance, two important features of the PVS proof assistant. We prove that this encoding is correct and that encoded proofs can be mechanically checked by Dedukti, a type checker for the ??-calculus modulo theory using rewriting

Deductive verification of requirements for event-driven architecture

The current paper presents the technology of processing of requirements for systems with event-driven architecture. The technology consists of the stages of formalization, formal verification and conversion to design specifications. The formalization is the formal description of events as formal specifications called basic protocols. The consistency and completeness of basic protocols, safety properties and user-defined properties are verified. The deductive tools for dynamic and static checking are used for detection of properties violation. The method of enlargement allows reducing the complexity of proving and solving. Formal presentation of requirements allows converting them to SDL\UML specifications and generating the test suite. The technology is realized in IMS system and applied in more than 50 projects of telecommunication, networking, microprocessing and automotive systems

Jahresbericht 2018

Der Jahresbericht 2018 enthält Informationen über die Aktivitäten des Deutschen Forschungsinstituts für öffentliche Verwaltung im Jahr 2017

Strategic Issues, Problems and Challenges in Inductive Theorem Proving

Abstract(Automated) Inductive Theorem Proving (ITP) is a challenging field in automated reasoning and theorem proving. Typically, (Automated) Theorem Proving (TP) refers to methods, techniques and tools for automatically proving general (most often first-order) theorems. Nowadays, the field of TP has reached a certain degree of maturity and powerful TP systems are widely available and used. The situation with ITP is strikingly different, in the sense that proving inductive theorems in an essentially automatic way still is a very challenging task, even for the most advanced existing ITP systems. Both in general TP and in ITP, strategies for guiding the proof search process are of fundamental importance, in automated as well as in interactive or mixed settings. In the paper we will analyze and discuss the most important strategic and proof search issues in ITP, compare ITP with TP, and argue why ITP is in a sense much more challenging. More generally, we will systematically isolate, investigate and classify the main problems and challenges in ITP w.r.t. automation, on different levels and from different points of views. Finally, based on this analysis we will present some theses about the state of the art in the field, possible criteria for what could be considered as substantial progress, and promising lines of research for the future, towards (more) automated ITP

Rhein, Romantik, Reisen. : Der Ausflugs- und Erholungsreiseverkehr im Mittelrheintal im Kontext gesellschaftlichen Wandels (1890 bis 1970)

Das Mittelrheintal zwischen Bonn und Rüdesheim gehört zu den ältesten Rei-segebieten Deutschlands. Schon im 19. Jahrhundert strömten Besucher auf der Suche nach Erholung und Vergnügen so zahlreich in die Kleinstädte entlang des Flusses, dass Hotels und Restaurants häufig ebenso überfüllt waren wie die Rheindampfer. Bis vor Ausbruch des Ersten Weltkriegs etablierte sich ne-ben dem Übernachtungsreiseverkehr ein schichtübergreifender Tagesausflugs-verkehr, wodurch erstmals „moderne“ Strukturen im rheinischen Fremdenver-kehr sichtbar wurden. Seitdem war der Ausflugs- und Erholungsreiseverkehr im Mittelrheintal Wandlungsprozessen unterworfen, die in starker Abhängigkeit zu politischen Entwicklungen, verkehrstechnischen Fortschritten und individuellen und allgemeinen Konsummöglichkeiten und -gewohnheiten der Reisenden standen. Dabei lassen sich sowohl durchgängig den Rheintourismus prägende Besonderheiten feststellen wie auch einschneidende Zäsuren und Brüche. Nach dem Einschnitt des Ersten Weltkriegs blieb das touristische Geschehen am Mittelrhein durch die politischen Rahmenbedingungen, die Rheinlandbeset-zung und die wirtschaftliche und soziale Not bis Anfang der Zwanziger Jahre erheblich eingeschränkt. Seit den sogenannten „Goldenen Zwanzigern“ gehör-ten allerdings Tagesausflüge und Kurzurlaube in gesteigertem Maße zum Be-standteil eines modernen Lebensstils, der sich auch auf die weniger begüterten Gesellschaftsschichten ausweitete. Insbesondere die Ausflugsgäste wurden am Mittelrhein zahlreicher, zugleich aber auch wesentlich sparsamer. Während der Weltwirtschaftskrise zeigte sich in den nur gering zurückgehenden Besucher-zahlen, wie sehr sich das Reisen inzwischen in den verbreiteten Lebensge-wohnheiten verankert hatte. Seit 1933 griff der Nationalsozialismus – wie in die meisten Lebensbereiche – auch in die Belange des Fremdenverkehrs ein. In gesellschafts- wie auch in außenpolitischer Hinsicht wurde der Fremdenverkehr in seinem propagandistischen Wert erkannt. Subventionierte „Kraft-durch-Freude“-Reisen traten neben den herkömmlichen Tourismus, während die Fremdenverkehrsgemeinden dazu angehalten wurden, gegenüber ausländi-schen Gästen als Aushängeschild für deutsche Tugenden zu wirken. Hierbei rückten die regionalen Verkehrsverbände in eine schwierige Mittlerfunktion zwi-schen nationalsozialistischer Politik und Fremdenverkehrsbranche. Nach dem erneuten Zusammenbruch während des Zweiten Weltkriegs kam es in den Jah-ren des sogenannten „Wirtschaftswunders“ auf Grundlage der allgemeinen Verbesserungen der wirtschaftlichen und sozialen Lage auch im mittelrheini-schen Fremdenverkehr zu einem enormen Aufschwung. In dieser Glanzzeit des Ausflugs- und Erholungsreiseverkehrs am Mittelrhein ging der quantitative Auf-schwung mit qualitativen Veränderungen des Reiseverhaltens einher: einer wachsenden Bedeutung des Autoreiseverkehrs, einer deutlichen Verkürzung der Aufenthaltsdauer, einer Zunahme des Tagesausflugsverkehrs und dem auf-kommenden Campingtourismus. Seit den ausgehenden 50er Jahren stagnier-ten die Besucherzahlen. Ganz entgegen dem Trend des allgemeinen Reise-booms blieben am Rhein in den 60er Jahren die zahlreichen Bemühungen um Verbesserungen oder Differenzierungen des touristischen Angebots überwie-gend wirkungslos. Auf Grundlage der Auswertung umfangreichen Archivmaterials umreißt die Ar-beit die Entwicklung des Fremdenverkehrs im Mittelrheintal vom ausgehenden 19. Jahrhundert bis in die 1960er Jahre hinein und erarbeitet dabei einige präg-nante Besonderheiten des Rheintourismus: die herausragende Bedeutung des Ausländerreiseverkehrs, der seit Beginn, insbesondere aber in den 1950er Jah-ren zur tragenden Säule der Entwicklung wurde; die nachhaltige Bedeutung der verkehrstechnischen Entwicklung bei der Rheinschifffahrt und dem Automobil; spürbare Kontinuitäten über die politischen Zäsuren hinweg, vor allem im Hin-blick auf die typischen Werbeklischees für den Rheintourismus; die andauern-den Versuche der Verkehrsverbände und -vereine, auf den Charakter des Fremdenverkehrs und das Verhalten der Touristen Einfluss zu nehmen; und schließlich die generelle Charakterisierung des Mittelrheintales als typisches Durchreiseland mit einer wachsenden Dominanz des Tagesausflugsverkehrs und einer mangelnden Etablierung pauschaltouristischer Angebotsstrukturen.Rhine. Romanticism. Travelling. The travel and leisure history in the Rhine Valley in the context of societal change (1890 until 1970) The Rhine Valley between the cities of Rüdesheim in the south and Bonn in the north is one of Germany’s oldest travel regions. As early as in the 18th century visitors searching relaxation and adventure poured into the small towns along-side the river, jamming hotels and restaurants as well as the riverboats. Until the break of World War One a day-trip market that bridged all social classes emerged alongside the overnight market thus showing “modern” tourism struc-tures in the region for the first time. Since then the day-trip and leisure travel in the Rhine Valley was closely linked to political and infrastructure developments as well as to individual and common (financial) backgrounds and consumption habits. One can identify individual characteristics that shape the Rhine Valley tourism throughout the decades on the one hand and shifts and breaks on the other. Due to the political context, the occupation of the Rhineland and the economical and social misery following World War One the tourism activities in the Rhine Valley had slowed down significantly in the early 20’s. Since the so called “roar-ing twenties” short day- and overnight trips increasingly belonged to a modern lifestyle which also was pursued by less affluent social classes. Especially day-trip guests increasingly travelled to the Rhine Valley, however at the same time spending less money. The fact that visitor numbers only declined marginally during the world economic crises shows how much “travelling” had at that time become part of a broad lifestyle. Following 1933 the Nazis tried to actively shape the tourism industry just as much as other societal areas recognizing the propaganda-potential both for the areas of domestic- and foreign policy. In this process subsidised “Kraft-durch-Freude” trips developed alongside conventional tourism, whereas communities where told to promote German virtues towards foreign travellers. The regional travelling associations thus were stuck in a com-plicated middle position with pressure applied from Nazi-policies from one side and that of the tourism industry from the other. After another breakdown during the Second World War the following years of the “Wirtschaftswunder” going along with fast-paced economic recovery and social improvements marked the basis for an enormous upswing of tourism in the area. This “golden era” of tour-ism in the Rhine Valley was marked by the fact that the quantitative upswing went alongside with qualitative changes of travelling habits: an increasing im-portance of automobile-based tourism, a clear shortening of the duration of stays, an increase of day-travelling and the emerging camping tourism. Since the late 50’s the visitor numbers stagnated. Contrasting the general boom in the travelling industry the efforts of the involved parties in the Rhine Valley to im-prove and differentiate the tourism offerings proved to have hardly any effect. On the basis of the analysis of extensive archive materials the dissertation por-trays the development of tourism in the Rhine Valley starting in the late 18th century until the 1960’s while compiling some special characteristics of the Rhine tourism: the tremendous importance of foreign visitors, that had shaped tourism in the region ever since the beginning, however becoming the key com-ponent of it in the 1950’s; the sustained development of the Rhine shipping in-dustry and automobile travel; obvious continuities bridging political breaks and upheavals, especially regarding the typical marketing clichés for Rhine tourism; the ever-repeating efforts of the travelling associations- and clubs to shape the character of tourism and the habits of tourists in the regions; and finally the general evaluation of the Rhine Valley as a typical region of journey-through tourism with a growing dominance of day-tourism and the lacking establishment of all-inclusive offerings. [for the translation very special thanks to Sean Harris

Geomechanical-numerical modeling of the crustal stress state of Germany

The stress state in the earth crust is an important quantity for many scientific and technical questions, e.g., seismic hazard assessment, borehole stability and underground storage. However, the level of knowledge about the recent stress field in Germany is still limited. There are basically two larger data sets available: (1) the World Stress Map (WSM) providing mainly information about the orientation of the maximum horizontal stress (SHmax) as well as the stress regime and (2) a stress magnitude database of Germany providing magnitude information about the individual components of the absolute stress tensor. However, the data are sparse, pointwise and unequally distributed. Therefore, a continuous prediction of the recent crustal stress state of Germany by linear interpolation between these data points is not suitable, in particular due to vertical and lateral inhomogeneities, e.g., mechanical properties, or faults leading to stress variations within in the crust. The presented cumulative dissertation is part of the SpannEnD project that aims to enhance the state of knowledge of the stress field in Germany. This dissertation contains three manuscripts: two dealing with the continuous prediction of the recent crustal stress state of Germany by large scale (1000 x 1250 x 100 km3) geomechanical-numerical models and one with the analysis of slip tendency (TS) of faults in Germany using results of one of these models. The two geomechanical-numerical models contain units describing the present geological conditions, which are parameterized with individual rock properties. Linear elasticity is assumed and the Finite Element Method (FEM) is used to solve the equilibrium of forces. The models enable a continuous prediction of the absolute stress state based on continuum mechanics within the upper lithosphere for the entire area of Germany for the first time. The first model presented in this cumulative dissertation contains seven units: a sedimentary unit, four laterally overlapping units of the upper crust, the lower crust and parts of the lithospheric mantle. It is calibrated against magnitudes of the minimum horizontal stress (Shmin) and compared with orientations of SHmax of the WSM and some additional data. The results show an overall good fit to the orientation of SHmax with a mean of the absolute deviations of 15.6° and a median of 5.6° and to the Shmin magnitudes with a mean of the absolute differences of 3.3 MPa used for calibration. However, the SHmax magnitudes show some larger differences especially too low values within the upper part of the model. The second model is an improved version of the first model with focus on a higher stratigraphic resolution of the sedimentary unit, containing 22 units. In combination with an 18-time higher mesh resolution and an additional calibration with SHmax magnitudes the results show an overall good fit to the magnitudes of all principal stresses (Shmin, SHmax and the vertical stress (SV)) and the WSM orientation data. This is indicated by absolute differences of 0.0 MPa for SV, 4.6 MPa for Shmin and 6.4 MPa for SHmax and by a median of 0.3° and absolute differences of 11.9° for the SHmax orientations within the central part. The third manuscript shows a possible application for the results of a large-scale geomechanical-numerical model. It is a TS analysis of faults for Germany using the results of the first model of this study and three different sets of faults with increasing complexities. The analysis show a good spatial agreement between the calculated TS and earthquakes within the study area. However, the fit between the depth of earthquake occurrence and the highest predicted TS show some discrepancies. In general, the study shows the influence of the fault geometry, the fault orientation in relation to the stress field and the crucial influence of the pore pressure. The results of this cumulative dissertation are a step towards a better understanding of the recent stress field of Germany. By two geomechanical models providing - for the first time the 3D stress tensor - and results, which are in good agreement with different calibration and comparison data sets. However, there are still some local and few general deviations that need to be further investigated, for example, with smaller more complex models, for which the stress field of this study can be used as an initial stress state

FLAVERS: a Finite State Verification Technique for Software Systems

Software systems are increasing in size and complexity and, subsequently, are becoming ever more difficult to validate. Finite State Verification (FSV) has been gaining credibility and attention as an alternative to testing and to formal verification approaches based on theorem proving. There has recently been a great deal of excitement about the potential for FSV approaches to prove properties about hardware descriptions but, for the most part, these approaches do not scale adequately to handle the complexity usually found in software. In this paper, we describe an FSV approach that creates a compact and conservative, but imprecise, model of the system being analyzed, and then assists the analyst in adding additional details as guided by previous analysis results. This paper describes this approach and a prototype implementation, called FLAVERS, presents a detailed example, and then provides some experimental results demonstrating scalability

Wilhelm Groener, Officering, and the Schlieffen Plan

This dissertation analyzes the career and attitudes of Wilhelm Groener (1867-1939), whom it uses as a vehicle for understanding the Imperial German army officer corps and the assumptions that guided the General Staff war planning process that culminated in the Schlieffen Plan and the German invasion of Belgium and France in 1914