A Pebbling Comonad for Finite Rank and Variable Logic, and an Application to the Equirank-variable Homomorphism Preservation Theorem
Author(s) -
Thomas Paine
Publication year - 2020
Publication title -
electronic notes in theoretical computer science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.242
H-Index - 60
ISSN - 1571-0661
DOI - 10.1016/j.entcs.2020.09.010
Subject(s) - homomorphism , mathematics , rank (graph theory) , variable (mathematics) , bounded function , quantifier (linguistics) , tree (set theory) , discrete mathematics , quantifier elimination , algebra over a field , combinatorics , pure mathematics , computer science , mathematical analysis , artificial intelligence
In this paper we recast the proof of Rossman's equirank homomorphism preservation theorem using comonadic formulations of bounded quantifier rank and variable count (and dually tree width and tree-depth), and work towards generalisation of it that simultaneously preserves quantifier rank and variable count. Along the way, we give an exposition of the required comonads, showing how their properties arise.
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