✦ LIBER ✦
Duality Theorems for Finite Structures (Characterising Gaps and Good Characterisations)
✍ Scribed by Jaroslav Nešetřil; Claude Tardif
- Publisher
- Elsevier Science
- Year
- 2000
- Tongue
- English
- Weight
- 161 KB
- Volume
- 80
- Category
- Article
- ISSN
- 0095-8956
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✦ Synopsis
We provide a correspondence between the subjects of duality and density in classes of finite relational structures. The purpose of duality is to characterise the structures C that do not admit a homomorphism into a given target B by the existence of a homomorphism from a structure A into C. Density is the order-theoretic property of containing no covers (or ``gaps''). We show that the covers in the skeleton of a category of finite relational models correspond naturally to certain instances of duality statements, and we characterise these covers.