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Discrete Mathematics
Volume 277, Issues 1-3, 28 February 2004, Pages 193-218
 
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doi:10.1016/S0012-365X(03)00152-3    How to Cite or Link Using DOI (Opens New Window)
Copyright © 2003 Elsevier B.V. All rights reserved.

0-Centred and 0-ubiquitously graceful trees

Frank Van BusselE-mail The Corresponding Author

Department of Computer Science, University of Toronto, Toronto, Ont., Canada

Received 18 June 2002; 
revised 13 February 2003; 
accepted 10 March 2003. ;
Available online 11 June 2003.

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Abstract

A tree T is k-centred graceful if it has a graceful labelling f such that f assigns the label k to the centre vertex (or one of the centres if the tree has odd diameter); similarly, a graph G is k-ubiquitously graceful if for every vertex vset membership, variantV(G) there is a graceful labelling f of G such that f(v)=k. In this paper we isolate a small and easily characterized subset of trees that are not 0-centred graceful, and a larger but still very manageable set of non-0-ubiquitously graceful trees; these we denote by Image and Image , respectively. It is shown that all trees of diameter less-than-or-equals, slant4 that are not in Image are 0-centred graceful, and all that are not in Image are 0-ubiquitously graceful. Upon consideration of some very intriguing empirical data we conjecture that these results in fact extend to all trees.

Author Keywords: Graph labelling; Graceful tree conjecture

Article Outline

1. Introduction
1.1. Labelling vertices “gracefully”
1.2. New results
2. Empirical results
3. Trees of diameter 4 with centre degree 2
4. Other trees of diameter 4
5. Trees that are 0-ubiquitously graceful
5.1. Closing remarks
References









Discrete Mathematics
Volume 277, Issues 1-3, 28 February 2004, Pages 193-218
 
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