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Generalised Type Preprocessing for Integrated Subtyping
(2025) Tang, Alvin
Subtyping is a common feature that organises types into hierarchies, which is used for encoding various forms of polymorphism. Subtype relations are typically defined syntactically using axioms and inference rules, but they do not always directly translate to a decision procedure. Therefore, in addition to a declarative system that consists of more modular and intuitive rules, it is a normal practice to devise an equivalent reductive system that corresponds to an algorithm. However, some desirable relations, such as distributivity, cannot be easily incorporated into the latter. This work presents the integrated subtyping framework. Upon standardising the methodology to prove equivalence between declarative and reductive subtyping, we present a systematic way to extend subtyping systems through a type preprocessing scheme. The normalisation scheme is specified by the framework user as integrator functions. We outline a set of requirements and, in turn, offer guarantees regarding the reflexivity, transitivity, equivalence and decidability of the extended systems. With the mutually inductive design, we establish the (co)monadic properties of the integrators, abstract away complexities and decompose the obligations for the user into smaller, more manageable proof goals. Following the metatheory, we study the practical applicability of integrated subtyping with framework instantiations involving union and intersection types as well as predicative higher-rank polymorphic types, drawing reference to Scala 3’s type system. As we promote modularity and composability, the framework reduces the need for repetitive, tedious proofs. We therefore envision the framework to be a flexible tool to develop more expressive programming languages by supporting decidable subtyping, which is increasingly significant for features such as gradual typing.
Disentangling Limits to Arbitrage: Empirical Evidence on Volatility-Based Limits and Cost-Based Limits
(2025) Zhao, Yueyang
This study investigates how limits to arbitrage contribute to persistent mispricing by decomposing them into cost-based and volatility-based components. Cost-based limits arise from borrowing costs, lending-market scarcity, and lending fragility, while volatility-based limits capture risk-related frictions such as position size constraints and margin-call risk. Using U.S. equity data from May 2002 to December 2016, this study integrates double-sorting, Fama–MacBeth cross-sectional regressions, and the Hou and Loh (2016) decomposition framework to quantify the independent and relative effects of these limits. The results show that volatility-based limits exert a significant additional effect in preventing mispricing correction on top of cost-based limits. Decomposition analysis reveals that the relative contribution ratio of volatility-based to cost based components is about 3:7, indicating that mispricing persistence is not fully driven by cost-based limits alone. Robustness tests using value-weighted portfolios, portfolio-level decomposition, alternative factor models, and interpolation methods confirm the consistency of these findings. Overall, the evidence demonstrates that volatility-based limits represent a distinct and economically meaningful dimension of limits to arbitrage. Recognizing both cost-based and volatility-based limits provides a more comprehensive understanding of why mispricing persists in financial markets.
Regulation of Corporate Activity in the Space Sector
(Santa Clara Law School, 2022) Kamalnath, Akshaya; Sarkar, Hitoishi
This article argues that commercialisation of space coupled with technological innovation call for a regulatory approach beyond (and complementary to) the treaty regime offered by international law. The rapid technological advances in the financial sector and corresponding regulatory innovations make fintech regulation a likely candidate to draw lessons from for the nascent New Space sector. The article draws from the financial technology (fintech) sector and proposes that some lessons about initial regulation via sandboxes and sandbox bridges are useful in the space sector. At the domestic level the article proposes regulatory sandboxes to enable innovation while ensuring the necessary safeguards; and at the multi-national level, it proposes cooperation between regulators in various space-faring nations along the lines of sandbox bridges used in the fintech sector. Since different states have varying levels of space sector activity, this article makes broad recommendations with pointers that identify aspects that are more suitable to certain types of jurisdictions than others.
Where Are Our By-Laws? Community Innovation and Lost Opportunities in Urban Fiji
(Canberra, ACT: Dept. of Pacific Affairs, Coral Bell School of Asia Pacific Affairs, The Australian National University, 2025-11-28) Dinnen, Sinclair; Forsyth, Miranda
Jittu Estate is one of Suva’s oldest and largest informal settlements with population estimates ranging from 3,500 to 10,000, the higher figure being offered by community leaders and officials that we spoke with. Despite congested living conditions and challenges around basic utilities, the settlement’s central location makes it an attractive destination for low-income households and recent migrants to the nation’s capital. Over the years, the settlement acquired a reputation for social order problems including disorderly conduct, family violence (Khan 2010) and petty crime. It has also been seen as a haven for stolen goods and, more recently, drug dealing and abuse. As a result, the police classified Jittu Estate as a ‘Red Zone’, denoting a high crime area. This reputation followed residents when they ventured outside the community, such that they were often the first to be blamed when something went missing.