9 Search Results for "D�az-Caro, Alejandro"

Document
Invited Talk
DOI: 10.4230/LIPIcs.OPODIS.2023.1
From Consensus Research to Redbelly Network Pty Ltd (Invited Talk)

Authors: Vincent Gramoli

Published in: LIPIcs, Volume 286, 27th International Conference on Principles of Distributed Systems (OPODIS 2023)

Abstract
Designing and implementing correctly a blockchain system requires collaborations across places and research fields. Redbelly, a company across Australia, India and USA, illustrates well this idea. It started in 2005 at OPODIS, where we published the Reconfigurable Distributed Storage to replace distributed participants offering a service without disrupting its availability. This line of work [V. Gramoli et al., 2021] was instrumental to reconfigure blockchains without introducing hard forks. The research on the consensus problem we initiated at IRISA [V. Gramoli, 2022] led to rethinking PBFT-like algorithms for the context of blockchain by getting rid of the leader that can act as the bottleneck of large networks [V. Gramoli and Q. Tang, 2023]. Our work on security led to disclosing vulnerabilities in Ethereum [Parinya Ekparinya et al., 2020] and then motivated us to formally verify blockchain consensus [Nathalie Bertrand et al., 2022]. Our work at the frontier of economics [Michael Spain et al., 2019] led us to prevent front-running attacks [Pouriya Zarbafian and Vincent Gramoli, 2023] and to incentivize rational players to behave [Alejandro Ranchal-Pedrosa and Vincent Gramoli, 2022]. Our system work at Cornell and then at EPFL was foundational in experimenting blockchains across the globe [Vincent Gramoli et al., 2023]. Although not anticipated at the time, this series of work progressively led the University of Sydney and CSIRO, and later Redbelly Network Pty Ltd, to design the Redbelly Blockchain [Tyler Crain et al., 2021; Deepal Tennakoon et al., 2023], the platform of choice for compliant asset tokenisation.
Cite as

Vincent Gramoli. From Consensus Research to Redbelly Network Pty Ltd (Invited Talk). In 27th International Conference on Principles of Distributed Systems (OPODIS 2023). Leibniz International Proceedings in Informatics (LIPIcs), Volume 286, pp. 1:1-1:2, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)

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@InProceedings{gramoli:LIPIcs.OPODIS.2023.1,
  author =	{Gramoli, Vincent},
  title =	{{From Consensus Research to Redbelly Network Pty Ltd}},
  booktitle =	{27th International Conference on Principles of Distributed Systems (OPODIS 2023)},
  pages =	{1:1--1:2},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-308-9},
  ISSN =	{1868-8969},
  year =	{2024},
  volume =	{286},
  editor =	{Bessani, Alysson and D\'{e}fago, Xavier and Nakamura, Junya and Wada, Koichi and Yamauchi, Yukiko},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2023.1},
  URN =		{urn:nbn:de:0030-drops-194915},
  doi =		{10.4230/LIPIcs.OPODIS.2023.1},
  annote =	{Keywords: Innovations, Commercialisation}
}
Document
DOI: 10.4230/LIPIcs.OPODIS.2023.21
Fault-Tolerant Computing with Unreliable Channels

Authors: Alejandro Naser-Pastoriza, Gregory Chockler, and Alexey Gotsman

Published in: LIPIcs, Volume 286, 27th International Conference on Principles of Distributed Systems (OPODIS 2023)

Abstract
We study implementations of basic fault-tolerant primitives, such as consensus and registers, in message-passing systems subject to process crashes and a broad range of communication failures. Our results characterize the necessary and sufficient conditions for implementing these primitives as a function of the connectivity constraints and synchrony assumptions. Our main contribution is a new algorithm for partially synchronous consensus that is resilient to process crashes and channel failures and is optimal in its connectivity requirements. In contrast to prior work, our algorithm assumes the most general model of message loss where faulty channels are flaky, i.e., can lose messages without any guarantee of fairness. This failure model is particularly challenging for consensus algorithms, as it rules out standard solutions based on leader oracles and failure detectors. To circumvent this limitation, we construct our solution using a new variant of the recently proposed view synchronizer abstraction, which we adapt to the crash-prone setting with flaky channels.
Cite as

Alejandro Naser-Pastoriza, Gregory Chockler, and Alexey Gotsman. Fault-Tolerant Computing with Unreliable Channels. In 27th International Conference on Principles of Distributed Systems (OPODIS 2023). Leibniz International Proceedings in Informatics (LIPIcs), Volume 286, pp. 21:1-21:21, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)

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@InProceedings{naserpastoriza_et_al:LIPIcs.OPODIS.2023.21,
  author =	{Naser-Pastoriza, Alejandro and Chockler, Gregory and Gotsman, Alexey},
  title =	{{Fault-Tolerant Computing with Unreliable Channels}},
  booktitle =	{27th International Conference on Principles of Distributed Systems (OPODIS 2023)},
  pages =	{21:1--21:21},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-308-9},
  ISSN =	{1868-8969},
  year =	{2024},
  volume =	{286},
  editor =	{Bessani, Alysson and D\'{e}fago, Xavier and Nakamura, Junya and Wada, Koichi and Yamauchi, Yukiko},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2023.21},
  URN =		{urn:nbn:de:0030-drops-195118},
  doi =		{10.4230/LIPIcs.OPODIS.2023.21},
  annote =	{Keywords: Consensus, network partitions, liveness, synchronizers}
}
Document
DOI: 10.4230/LIPIcs.FSCD.2023.11
Two Decreasing Measures for Simply Typed λ-Terms

Authors: Pablo Barenbaum and Cristian Sottile

Published in: LIPIcs, Volume 260, 8th International Conference on Formal Structures for Computation and Deduction (FSCD 2023)

Abstract
This paper defines two decreasing measures for terms of the simply typed λ-calculus, called the 𝒲-measure and the 𝒯^{𝐦}-measure. A decreasing measure is a function that maps each typable λ-term to an element of a well-founded ordering, in such a way that contracting any β-redex decreases the value of the function, entailing strong normalization. Both measures are defined constructively, relying on an auxiliary calculus, a non-erasing variant of the λ-calculus. In this system, dubbed the λ^{𝐦}-calculus, each β-step creates a "wrapper" containing a copy of the argument that cannot be erased and cannot interact with the context in any other way. Both measures rely crucially on the observation, known to Turing and Prawitz, that contracting a redex cannot create redexes of higher degree, where the degree of a redex is defined as the height of the type of its λ-abstraction. The 𝒲-measure maps each λ-term to a natural number, and it is obtained by evaluating the term in the λ^{𝐦}-calculus and counting the number of remaining wrappers. The 𝒯^{𝐦}-measure maps each λ-term to a structure of nested multisets, where the nesting depth is proportional to the maximum redex degree.
Cite as

Pablo Barenbaum and Cristian Sottile. Two Decreasing Measures for Simply Typed λ-Terms. In 8th International Conference on Formal Structures for Computation and Deduction (FSCD 2023). Leibniz International Proceedings in Informatics (LIPIcs), Volume 260, pp. 11:1-11:19, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2023)

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@InProceedings{barenbaum_et_al:LIPIcs.FSCD.2023.11,
  author =	{Barenbaum, Pablo and Sottile, Cristian},
  title =	{{Two Decreasing Measures for Simply Typed \lambda-Terms}},
  booktitle =	{8th International Conference on Formal Structures for Computation and Deduction (FSCD 2023)},
  pages =	{11:1--11:19},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-277-8},
  ISSN =	{1868-8969},
  year =	{2023},
  volume =	{260},
  editor =	{Gaboardi, Marco and van Raamsdonk, Femke},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.FSCD.2023.11},
  URN =		{urn:nbn:de:0030-drops-179956},
  doi =		{10.4230/LIPIcs.FSCD.2023.11},
  annote =	{Keywords: Lambda Calculus, Rewriting, Termination, Strong Normalization, Simple Types}
}
Document
DOI: 10.4230/LIPIcs.ESA.2022.54
Improved Search of Relevant Points for Nearest-Neighbor Classification

Authors: Alejandro Flores-Velazco

Published in: LIPIcs, Volume 244, 30th Annual European Symposium on Algorithms (ESA 2022)

Abstract
Given a training set P ⊂ ℝ^d, the nearest-neighbor classifier assigns any query point q ∈ ℝ^d to the class of its closest point in P. To answer these classification queries, some training points are more relevant than others. We say a training point is relevant if its omission from the training set could induce the misclassification of some query point in ℝ^d. These relevant points are commonly known as border points, as they define the boundaries of the Voronoi diagram of P that separate points of different classes. Being able to compute this set of points efficiently is crucial to reduce the size of the training set without affecting the accuracy of the nearest-neighbor classifier. Improving over a decades-long result by Clarkson (FOCS'94), Eppstein (SOSA’22) recently proposed an output-sensitive algorithm to find the set of border points of P in 𝒪(n² + nk²) time, where k is the size of such set. In this paper, we improve this algorithm to have time complexity equal to 𝒪(nk²) by proving that the first phase of their algorithm, which requires 𝒪(n²) time, are unnecessary.
Cite as

Alejandro Flores-Velazco. Improved Search of Relevant Points for Nearest-Neighbor Classification. In 30th Annual European Symposium on Algorithms (ESA 2022). Leibniz International Proceedings in Informatics (LIPIcs), Volume 244, pp. 54:1-54:10, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2022)

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@InProceedings{floresvelazco:LIPIcs.ESA.2022.54,
  author =	{Flores-Velazco, Alejandro},
  title =	{{Improved Search of Relevant Points for Nearest-Neighbor Classification}},
  booktitle =	{30th Annual European Symposium on Algorithms (ESA 2022)},
  pages =	{54:1--54:10},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-247-1},
  ISSN =	{1868-8969},
  year =	{2022},
  volume =	{244},
  editor =	{Chechik, Shiri and Navarro, Gonzalo and Rotenberg, Eva and Herman, Grzegorz},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.ESA.2022.54},
  URN =		{urn:nbn:de:0030-drops-169922},
  doi =		{10.4230/LIPIcs.ESA.2022.54},
  annote =	{Keywords: nearest-neighbor classification, nearest-neighbor rule, decision boundaries, border points, relevant points}
}
Document
DOI: 10.4230/LIPIcs.FSCD.2022.21
Linear Lambda-Calculus is Linear

Authors: Alejandro Díaz-Caro and Gilles Dowek

Published in: LIPIcs, Volume 228, 7th International Conference on Formal Structures for Computation and Deduction (FSCD 2022)

Abstract
We prove a linearity theorem for an extension of linear logic with addition and multiplication by a scalar: the proofs of some propositions in this logic are linear in the algebraic sense. This work is part of a wider research program that aims at defining a logic whose proof language is a quantum programming language.
Cite as

Alejandro Díaz-Caro and Gilles Dowek. Linear Lambda-Calculus is Linear. In 7th International Conference on Formal Structures for Computation and Deduction (FSCD 2022). Leibniz International Proceedings in Informatics (LIPIcs), Volume 228, pp. 21:1-21:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2022)

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@InProceedings{diazcaro_et_al:LIPIcs.FSCD.2022.21,
  author =	{D{\'\i}az-Caro, Alejandro and Dowek, Gilles},
  title =	{{Linear Lambda-Calculus is Linear}},
  booktitle =	{7th International Conference on Formal Structures for Computation and Deduction (FSCD 2022)},
  pages =	{21:1--21:17},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-233-4},
  ISSN =	{1868-8969},
  year =	{2022},
  volume =	{228},
  editor =	{Felty, Amy P.},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.FSCD.2022.21},
  URN =		{urn:nbn:de:0030-drops-163024},
  doi =		{10.4230/LIPIcs.FSCD.2022.21},
  annote =	{Keywords: Proof theory, Lambda calculus, Linear logic, Quantum computing}
}
Document
DOI: 10.4230/LIPIcs.ESA.2021.44
Boundary-Sensitive Approach for Approximate Nearest-Neighbor Classification

Authors: Alejandro Flores-Velazco and David M. Mount

Published in: LIPIcs, Volume 204, 29th Annual European Symposium on Algorithms (ESA 2021)

Abstract
The problem of nearest-neighbor classification is a fundamental technique in machine-learning. Given a training set P of n labeled points in ℝ^d, and an approximation parameter 0 < ε ≤ 1/2, any unlabeled query point should be classified with the class of any of its ε-approximate nearest-neighbors in P. Answering these queries efficiently has been the focus of extensive research, proposing techniques that are mainly tailored towards resolving the more general problem of ε-approximate nearest-neighbor search. While the latest can only hope to provide query time and space complexities dependent on n, the problem of nearest-neighbor classification accepts other parameters more suitable to its analysis. Such is the number k_ε of ε-border points, which describes the complexity of boundaries between sets of points of different classes. This paper presents a new data structure called Chromatic AVD. This is the first approach for ε-approximate nearest-neighbor classification whose space and query time complexities are only dependent on ε, k_ε and d, while being independent on both n and Δ, the spread of P.
Cite as

Alejandro Flores-Velazco and David M. Mount. Boundary-Sensitive Approach for Approximate Nearest-Neighbor Classification. In 29th Annual European Symposium on Algorithms (ESA 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 204, pp. 44:1-44:15, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)

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@InProceedings{floresvelazco_et_al:LIPIcs.ESA.2021.44,
  author =	{Flores-Velazco, Alejandro and Mount, David M.},
  title =	{{Boundary-Sensitive Approach for Approximate Nearest-Neighbor Classification}},
  booktitle =	{29th Annual European Symposium on Algorithms (ESA 2021)},
  pages =	{44:1--44:15},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-204-4},
  ISSN =	{1868-8969},
  year =	{2021},
  volume =	{204},
  editor =	{Mutzel, Petra and Pagh, Rasmus and Herman, Grzegorz},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.ESA.2021.44},
  URN =		{urn:nbn:de:0030-drops-146252},
  doi =		{10.4230/LIPIcs.ESA.2021.44},
  annote =	{Keywords: approximate nearest-neighbor searching, nearest-neighbor classification, geometric data structures, space-time tradeoffs}
}
Document
DOI: 10.4230/LIPIcs.FSCD.2019.14
Proof Normalisation in a Logic Identifying Isomorphic Propositions

Authors: Alejandro Díaz-Caro and Gilles Dowek

Published in: LIPIcs, Volume 131, 4th International Conference on Formal Structures for Computation and Deduction (FSCD 2019)

Abstract
We define a fragment of propositional logic where isomorphic propositions, such as A wedge B and B wedge A, or A ==> (B wedge C) and (A ==> B) wedge (A ==> C) are identified. We define System I, a proof language for this logic, and prove its normalisation and consistency.
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Alejandro Díaz-Caro and Gilles Dowek. Proof Normalisation in a Logic Identifying Isomorphic Propositions. In 4th International Conference on Formal Structures for Computation and Deduction (FSCD 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 131, pp. 14:1-14:23, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2019)

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@InProceedings{diazcaro_et_al:LIPIcs.FSCD.2019.14,
  author =	{D{\'\i}az-Caro, Alejandro and Dowek, Gilles},
  title =	{{Proof Normalisation in a Logic Identifying Isomorphic Propositions}},
  booktitle =	{4th International Conference on Formal Structures for Computation and Deduction (FSCD 2019)},
  pages =	{14:1--14:23},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-107-8},
  ISSN =	{1868-8969},
  year =	{2019},
  volume =	{131},
  editor =	{Geuvers, Herman},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.FSCD.2019.14},
  URN =		{urn:nbn:de:0030-drops-105210},
  doi =		{10.4230/LIPIcs.FSCD.2019.14},
  annote =	{Keywords: Simply typed lambda calculus, Isomorphisms, Logic, Cut-elimination, Proof-reduction}
}
Document
DOI: 10.4230/LIPIcs.ICALP.2018.113
Almost Sure Productivity

Authors: Alejandro Aguirre, Gilles Barthe, Justin Hsu, and Alexandra Silva

Published in: LIPIcs, Volume 107, 45th International Colloquium on Automata, Languages, and Programming (ICALP 2018)

Abstract
We introduce Almost Sure Productivity (ASP), a probabilistic generalization of the productivity condition for coinductively defined structures. Intuitively, a probabilistic coinductive stream or tree is ASP if it produces infinitely many outputs with probability 1. Formally, we define ASP using a final coalgebra semantics of programs inspired by Kerstan and König. Then, we introduce a core language for probabilistic streams and trees, and provide two approaches to verify ASP: a syntactic sufficient criterion, and a decision procedure by reduction to model{-}checking LTL formulas on probabilistic pushdown automata.
Cite as

Alejandro Aguirre, Gilles Barthe, Justin Hsu, and Alexandra Silva. Almost Sure Productivity. In 45th International Colloquium on Automata, Languages, and Programming (ICALP 2018). Leibniz International Proceedings in Informatics (LIPIcs), Volume 107, pp. 113:1-113:15, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2018)

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@InProceedings{aguirre_et_al:LIPIcs.ICALP.2018.113,
  author =	{Aguirre, Alejandro and Barthe, Gilles and Hsu, Justin and Silva, Alexandra},
  title =	{{Almost Sure Productivity}},
  booktitle =	{45th International Colloquium on Automata, Languages, and Programming (ICALP 2018)},
  pages =	{113:1--113:15},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-076-7},
  ISSN =	{1868-8969},
  year =	{2018},
  volume =	{107},
  editor =	{Chatzigiannakis, Ioannis and Kaklamanis, Christos and Marx, D\'{a}niel and Sannella, Donald},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.ICALP.2018.113},
  URN =		{urn:nbn:de:0030-drops-91174},
  doi =		{10.4230/LIPIcs.ICALP.2018.113},
  annote =	{Keywords: Coinduction, Probabilistic Programming, Productivity}
}
Document
DOI: 10.4230/LIPIcs.STACS.2011.380
A Fast Algorithm for Multi-Machine Scheduling Problems with Jobs of Equal Processing Times

Authors: Alejandro Lopez-Ortiz and Claude-Guy Quimper

Published in: LIPIcs, Volume 9, 28th International Symposium on Theoretical Aspects of Computer Science (STACS 2011)

Abstract
Consider the problem of scheduling a set of tasks of length p without preemption on $m$ identical machines with given release and deadline times. We present a new algorithm for computing the schedule with minimal completion times and makespan. The algorithm has time complexity O(min(1,p/m)n^2) which improves substantially over the best known algorithm with complexity O(mn^2).
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Alejandro Lopez-Ortiz and Claude-Guy Quimper. A Fast Algorithm for Multi-Machine Scheduling Problems with Jobs of Equal Processing Times. In 28th International Symposium on Theoretical Aspects of Computer Science (STACS 2011). Leibniz International Proceedings in Informatics (LIPIcs), Volume 9, pp. 380-391, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2011)

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@InProceedings{lopezortiz_et_al:LIPIcs.STACS.2011.380,
  author =	{Lopez-Ortiz, Alejandro and Quimper, Claude-Guy},
  title =	{{A Fast Algorithm for Multi-Machine Scheduling Problems with Jobs of Equal Processing Times}},
  booktitle =	{28th International Symposium on Theoretical Aspects of Computer Science (STACS 2011)},
  pages =	{380--391},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-939897-25-5},
  ISSN =	{1868-8969},
  year =	{2011},
  volume =	{9},
  editor =	{Schwentick, Thomas and D\"{u}rr, Christoph},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.STACS.2011.380},
  URN =		{urn:nbn:de:0030-drops-30282},
  doi =		{10.4230/LIPIcs.STACS.2011.380},
  annote =	{Keywords: Scheduling}
}
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