First-order Definable Retraction Problems for Posets and Reflexive Graphs
نویسندگان
چکیده
منابع مشابه
Citation for Published Item: Use Policy First-order Definable Retraction Problems for Posets and Reflexive Graphs *
A retraction from a structure P to its substructure Q is a homomorphism from P onto Q that is the identity on Q. We present an algebraic condition which completely characterises all posets and all reflexive graphs Q with the following property: the class of all posets or reflexive graphs, respectively, that admit a retraction onto Q is first-order definable.
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ژورنال
عنوان ژورنال: Journal of Logic and Computation
سال: 2006
ISSN: 0955-792X,1465-363X
DOI: 10.1093/logcom/exl014