Core Concepts

Kraus' paradox is a surprising result in path categories, where truncation maps with homogeneous domain are monomorphisms.

Abstract

Introduction
Kraus' "magic trick" for recovering information from truncated types.
Working in Van den Berg-Moerdijk path categories with a univalent universe.
Path Categories
Definition of a path category.
Conditions for fibrations and weak equivalences.
Path objects and homotopy definitions.
hPropositions and Propositional Truncation
Definition of hPropositions and propositional truncation.
Propositions related to extensional path categories.
Univalence in Path Categories
Definition of univalence in path categories.
Theorem and proof regarding univalence.
Kraus' Paradox
Theorem regarding monomorphisms in coﬁbrations with homogeneous domain.
Examples and proofs in groupoids.
Worked Examples in Groupoids
Propositions and theorems related to groupoids.
Conclusion
Variations and generalizations of Kraus' paradox.
Surprising aspects of Kraus' paradox.

Stats

In [KECA17, Section 8.4] Kraus et al. gave a surprising proof.
Any coﬁbration with homogeneous domain is a monomorphism.
The category of groupoids is a path category.

Quotes

"Any coﬁbration with homogeneous domain is a monomorphism." - [KECA17]

Key Insights Distilled From

by Andrew W. Sw... at **arxiv.org** 03-28-2024

Deeper Inquiries

In the context of path categories, coﬁbrations with a homogeneous domain have a significant property - they are monomorphisms. This means that these coﬁbrations are injective in a specific sense within the path category framework. The concept of homogeneity plays a crucial role here, ensuring that these coﬁbrations exhibit a unique behavior that distinguishes them from other types of maps. While the definition of monomorphisms in traditional category theory focuses on injectivity, the notion of homotopy monomorphisms in path categories adds a layer of complexity by considering the homotopy equivalence aspect as well. This unique characteristic of coﬁbrations with homogeneous domains being monomorphisms showcases the intricate interplay between homogeneity, coﬁbrations, and the categorical structure within path categories.

When considering higher inductive types, such as W-types and nullification, a more refined formulation of Kraus' paradox could be explored. These types introduce additional complexities compared to traditional types, requiring a nuanced approach to understanding and applying Kraus' paradox within this context. One potential avenue for a better formulation could involve incorporating the recursive nature of point constructors in higher inductive types. By adapting the principles of Kraus' paradox to suit the recursive structures and unique characteristics of higher inductive types, a more tailored and effective formulation can be achieved. This adaptation would likely involve considering the specific properties and behaviors of higher inductive types, ensuring that the paradox is applied in a manner that aligns with the intricacies of these advanced type constructions.

Kraus' paradox can be viewed as surprising when considering the distinct definitions of injective maps in path categories. The paradox challenges conventional notions of injectivity by demonstrating that coﬁbrations with homogeneous domains are monomorphisms, highlighting a unique aspect of injective maps within the path category framework. The surprise arises from the contrast between the traditional understanding of injective maps as monomorphisms and the specialized concept of homotopy monomorphisms in path categories. This discrepancy underscores the richness and complexity of categorical structures, where different definitions and interpretations of fundamental concepts like injectivity can lead to unexpected results. The paradox serves as a thought-provoking example of how diverse perspectives within categorical frameworks can yield novel and counterintuitive outcomes, showcasing the depth and intricacy of mathematical reasoning in this context.

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