Digraph functors which admit both left and right adjoints

Foniok, J and Tardif, C (2014) Digraph functors which admit both left and right adjoints. Discrete Mathematics, 338. ISSN 0012-365X

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Abstract

For our purposes, two functors ΛΛ and ΓΓ are said to be adjoint if for any digraphs GG and HH, there exists a homomorphism of Λ(G)Λ(G) to HH if and only if there exists a homomorphism of GG to Γ(H)Γ(H). We investigate the right adjoints characterised by Pultr (1970). We find necessary conditions for these functors to admit right adjoints themselves. We give many examples where these necessary conditions are satisfied, and the right adjoint indeed exists. Finally, we discuss a connection between these right adjoints and homomorphism dualities.

Item Type:	Article
Peer-reviewed:	No
Date Deposited:	11 Mar 2016 15:09
Publisher:	Elsevier BV
Additional Information:	This is an Author Final Copy of a paper accepted for publication in Discrete Mathematics, published by and copyright Elsevier BV.
Divisions:	Faculties
URI:	https://e-space.mmu.ac.uk/id/eprint/601222
DOI:	https://doi.org/10.1016/j.disc.2014.10.018
ISSN	0012-365X

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