155 research outputs found
Children and Youth at Risk in Times of Transition: International and Interdisciplinary Perspectives
Children and youth belong to one of the most vulnerable groups in societies. This was the case even before the current humanitarian crises around the world which led millions of people and families to flee from wars, terror, poverty and exploitation. Minors have been denied human rights such as access to education, food and health services. They have been kidnapped, sold, manipulated, mutilated, killed, and injured. This has been and continues to be the case in both developed and developing countries, and it does not look as if the situation will improve in the near future. Rather, current geopolitical developments, political and economic uncertainties and instabilities seem to be increasing the vulnerability of minors, especially in the wars and armed conflicts currently being waged not only in Europe, but on almost every continent. How can risks children and youth are exposed to in times of transition be reduced? Which role do state agencies, non-governmental organisations, as well as children's coping strategies play in mitigating the vulnerabilities of minors? This volume addresses risks to which children and young people are exposed, especially in times of transition. The focus is on different groups of children in the European wartime and post-war societies of the Second World War, 'occupation children' in Germany, teenage National Socialist collaborators in Norway, and more recent cases such as child soldiers, refugee children, and children of European "Islamic State" fighters. The contributions come from international scholars and different academic disciplines (educational and social sciences, humanities, law, and international peace and conflict studies) and are based on historical, quantitative, and/or qualitative analyses.Kinder und Jugendliche gehören zu den am meisten gefährdeten Gruppen einer Gesellschaft. Dies war auch schon vor den aktuellen humanitären Krisen in der Welt der Fall, die Millionen von Menschen und Familien zur Flucht vor Kriegen, Terror, Armut und Ausbeutung veranlassten. Minderjährigen wurden Menschenrechte wie der Zugang zu Bildung, Nahrung und medizinischer Versorgung verweigert. Sie wurden entführt, verkauft, manipuliert, verstümmelt, getötet und verletzt. Dies war und ist sowohl in den Industrie- als auch in den Entwicklungsländern der Fall, und es sieht nicht so aus, als würde sich die Situation in naher Zukunft verbessern. Dieser Band befasst sich mit Risiken, denen Kinder und Jugendliche vor allem in Zeiten des Übergangs ausgesetzt sind. Im Mittelpunkt stehen verschiedene Gruppen von Kindern in den europäischen Kriegs- und Nachkriegsgesellschaften des Zweiten Weltkriegs, "Besatzungskinder" in Deutschland, jugendliche NS-Kollaborateure in Norwegen und neuere Fälle wie Kindersoldat*innen, Flüchtlingskinder und Kinder von europäischen "Islamischen Staat"-Kämpfer*innen. Die Beiträge stammen von internationalen Wissenschaftler*innen und verschiedenen akademischen Disziplinen (Erziehungs- und Sozialwissenschaften, Geisteswissenschaften, Rechtswissenschaften und internationale Friedens- und Konfliktstudien) und basieren auf historischen, quantitativen und/oder qualitativen Analysen
Trocq: Proof Transfer for Free, With or Without Univalence
Libraries of formalized mathematics use a possibly broad range of different
representations for a same mathematical concept. Yet light to major manual
input from users remains most often required for obtaining the corresponding
variants of theorems, when such obvious replacements are typically left
implicit on paper. This article presents Trocq, a new proof transfer framework
for dependent type theory. Trocq is based on a novel formulation of type
equivalence, used to generalize the univalent parametricity translation. This
framework takes care of avoiding dependency on the axiom of univalence when
possible, and may be used with more relations than just equivalences. We have
implemented a corresponding plugin for the Coq proof assistant, in the CoqElpi
meta-language. We use this plugin on a gallery of representative examples of
proof transfer issues in interactive theorem proving, and illustrate how Trocq
covers the spectrum of several existing tools, used in program verification as
well as in formalized mathematics in the broad sense
Nominal Recursors as Epi-Recursors: Extended Technical Report
We study nominal recursors from the literature on syntax with bindings and
compare them with respect to expressiveness. The term "nominal" refers to the
fact that these recursors operate on a syntax representation where the names of
bound variables appear explicitly, as in nominal logic. We argue that nominal
recursors can be viewed as epi-recursors, a concept that captures abstractly
the distinction between the constructors on which one actually recurses, and
other operators and properties that further underpin recursion.We develop an
abstract framework for comparing epi-recursors and instantiate it to the
existing nominal recursors, and also to several recursors obtained from them by
cross-pollination. The resulted expressiveness hierarchies depend on how
strictly we perform this comparison, and bring insight into the relative merits
of different axiomatizations of syntax. We also apply our methodology to
produce an expressiveness hierarchy of nominal corecursors, which are
principles for defining functions targeting infinitary non-well-founded terms
(which underlie lambda-calculus semantics concepts such as B\"ohm trees). Our
results are validated with the Isabelle/HOL theorem prover
Theorem Proving in Dependently-Typed Higher-Order Logic -- Extended Preprint
Higher-order logic HOL offers a very simple syntax and semantics for
representing and reasoning about typed data structures. But its type system
lacks advanced features where types may depend on terms. Dependent type theory
offers such a rich type system, but has rather substantial conceptual
differences to HOL, as well as comparatively poor proof automation support. We
introduce a dependently-typed extension DHOL of HOL that retains the style and
conceptual framework of HOL. Moreover, we build a translation from DHOL to HOL
and implement it as a preprocessor to a HOL theorem prover, thereby obtaining a
theorem prover for DHOL.Comment: 72 pages, The 29th International Conference on Automated Deduction
(CADE-29), July 1-5, 2023, Rome, Ital
Admissible types-to-PERs relativization in higher-order logic
Relativizing statements in Higher-Order Logic (HOL) from types to sets is useful for improving productivity when working with HOL-based interactive theorem provers such as HOL4, HOL Light and Isabelle/HOL. This paper provides the first comprehensive definition and study of types-to-sets relativization in HOL, done in the more general form of types-to-PERs (partial equivalence relations). We prove that, for a large practical fragment of HOL which includes container types such as datatypes and codatatypes, types-to-PERs relativization is admissible, in that the provability of the original, type-based statement implies the provability of its relativized, PER-based counterpart. Our results also imply the admissibility of a previously proposed axiomatic extension of HOL with local type definitions. We have implemented types-to-PERs relativization as an Isabelle tool that performs relativization of HOL theorems on demand
Semantic Foundations of Higher-Order Probabilistic Programs in Isabelle/HOL
Higher-order probabilistic programs are used to describe statistical models and machine-learning mechanisms. The programming languages for them are equipped with three features: higher-order functions, sampling, and conditioning. In this paper, we propose an Isabelle/HOL library for probabilistic programs supporting all of those three features. We extend our previous quasi-Borel theory library in Isabelle/HOL. As a basis of the theory, we formalize s-finite kernels, which is considered as a theoretical foundation of first-order probabilistic programs and a key to support conditioning of probabilistic programs. We also formalize the Borel isomorphism theorem which plays an important role in the quasi-Borel theory. Using them, we develop the s-finite measure monad on quasi-Borel spaces. Our extension enables us to describe higher-order probabilistic programs with conditioning directly as an Isabelle/HOL term whose type is that of morphisms between quasi-Borel spaces. We also implement the qbs prover for checking well-typedness of an Isabelle/HOL term as a morphism between quasi-Borel spaces. We demonstrate several verification examples of higher-order probabilistic programs with conditioning
Formal Methods for Trustworthy Voting Systems : From Trusted Components to Reliable Software
Voting is prominently an important part of democratic societies, and its outcome may have a dramatic and broad impact on societal progress. Therefore, it is paramount that such a society has extensive trust in the electoral process, such that the system’s functioning is reliable and stable with respect to the expectations within society. Yet, with or without the use of modern technology, voting is full of algorithmic and security challenges, and the failure to address these challenges in a controlled manner may produce fundamental flaws in the voting system and potentially undermine critical societal aspects.
In this thesis, we argue for a development process of voting systems that is rooted in and assisted by formal methods that produce transparently checkable evidence for the guarantees that the final system should provide so that it can be deemed trustworthy. The goal of this thesis is to advance the state of the art in formal methods that allow to systematically develop trustworthy voting systems that can be provenly verified. In the literature, voting systems are modeled in the following four comparatively separable and distinguishable layers: (1) the physical layer, (2) the computational layer, (3) the election layer, and (4) the human layer. Current research usually either mostly stays within one of those layers or lacks machine-checkable evidence, and consequently, trusted and understandable criteria often lack formally proven and checkable guarantees on software-level and vice versa.
The contributions in this work are formal methods that fill in the trust gap between the principal election layer and the computational layer by a reliable translation of trusted and understandable criteria into trustworthy software. Thereby, we enable that executable procedures can be formally traced back and understood by election experts without the need for inspection on code level, and trust can be preserved to the trustworthy system.
The works in this thesis all contribute to this end and consist in five distinct contributions, which are the following:
(I) a method for the generation of secure card-based communication schemes,
(II) a method for the synthesis of reliable tallying procedures,
(III) a method for the efficient verification of reliable tallying procedures,
(IV) a method for the computation of dependable election margins for reliable audits,
(V) a case study about the security verification of the GI voter-anonymization software.
These contributions span formal methods on illustrative examples for each of the three principal components, (1) voter-ballot box communication, (2) election method, and (3) election management, between the election layer and the computational layer.
Within the first component, the voter-ballot box communication channel, we build a bridge from the communication channel to the cryptography scheme by automatically generating secure card-based schemes from a small formal model with a parameterization of the desired security requirements. For the second component, the election method, we build a bridge from the election method to the tallying procedure by (1) automatically synthesizing a runnable tallying procedure from the desired requirements given as properties that capture the desired intuitions or regulations of fairness considerations, (2) automatically generating either comprehensible arguments or bounded proofs to compare tallying procedures based on user-definable fairness properties, and (3) automatically computing concrete election margins for a given tallying procedure, the collected ballots, and the computed election result, that enable efficient election audits. Finally, for the third and final component, the election management system, we perform a case study and apply state-of-the-art verification technology to a real-world e-voting system that has been used for the annual elections of the German Informatics Society (GI – “Gesellschaft für Informatik”) in 2019. The case study consists in the formal implementation-level security verification that the voter identities are securely anonymized and the voters’ passwords cannot be leaked.
The presented methods assist the systematic development and verification of provenly trustworthy voting systems across traditional layers, i.e., from the election layer to the computational layer. They all pursue the goal of making voting systems trustworthy by reliable and explainable formal requirements. We evaluate the devised methods on minimal card-based protocols that compute a secure AND function for two different decks of cards, a classical knock-out tournament and several Condorcet rules, various plurality, scoring, and Condorcet rules from the literature, the Danish national parliamentary elections in 2015, and a state-of-the-art electronic voting system that is used for the German Informatics Society’s annual elections in 2019 and following
Transport via Partial Galois Connections and Equivalences
Multiple types can represent the same concept. For example, lists and trees
can both represent sets. Unfortunately, this easily leads to incomplete
libraries: some set-operations may only be available on lists, others only on
trees. Similarly, subtypes and quotients are commonly used to construct new
type abstractions in formal verification. In such cases, one often wishes to
reuse operations on the representation type for the new type abstraction, but
to no avail: the types are not the same.
To address these problems, we present a new framework that transports
programs via equivalences. Existing transport frameworks are either designed
for dependently typed, constructive proof assistants, use univalence, or are
restricted to partial quotient types. Our framework (1) is designed for simple
type theory, (2) generalises previous approaches working on partial quotient
types, and (3) is based on standard mathematical concepts, particularly Galois
connections and equivalences. We introduce the notion of partial Galois
connections and equivalences and prove their closure properties under
(dependent) function relators, (co)datatypes, and compositions. We formalised
the framework in Isabelle/HOL and provide a prototype.
This is the extended version of "Transport via Partial Galois Connections and
Equivalences", 21st Asian Symposium on Programming Languages and Systems, 2023.Comment: 18 pages; will appear at 21st Asian Symposium on Programming
Languages and Systems, 202
Proof-theoretic Semantics for Intuitionistic Multiplicative Linear Logic
This work is the first exploration of proof-theoretic semantics for a substructural logic. It focuses on the base-extension semantics (B-eS) for intuitionistic multiplicative linear logic (IMLL). The starting point is a review of Sandqvist’s B-eS for intuitionistic propositional logic (IPL), for which we propose an alternative treatment of conjunction that takes the form of the generalized elimination rule for the connective. The resulting semantics is shown to be sound and complete. This motivates our main contribution, a B-eS for IMLL
, in which the definitions of the logical constants all take the form of their elimination rule and for which soundness and completeness are established
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