Cores of Countably Categorical Structures
Logic in Computer Science
2017-01-11 v2
Abstract
A relational structure is a core, if all its endomorphisms are embeddings. This notion is important for computational complexity classification of constraint satisfaction problems. It is a fundamental fact that every finite structure has a core, i.e., has an endomorphism such that the structure induced by its image is a core; moreover, the core is unique up to isomorphism. Weprove that every \omega -categorical structure has a core. Moreover, every \omega-categorical structure is homomorphically equivalent to a model-complete core, which is unique up to isomorphism, and which is finite or \omega -categorical. We discuss consequences for constraint satisfaction with \omega -categorical templates.
Cite
@article{arxiv.cs/0612069,
title = {Cores of Countably Categorical Structures},
author = {Manuel Bodirsky},
journal= {arXiv preprint arXiv:cs/0612069},
year = {2017}
}