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A diamond is a graph obtained by removing an edge from a complete graph on four vertices. A graph is diamond-free if it does not contain an induced diamond. The Diamond-free Edge Deletion problem asks to find whether there exist at most k edges in the input graph whose deletion results in a diamond-free graph. The problem was proved to be NP-complete and a polynomial kernel of O(k^4) vertices was found by Fellows et. al. (Discrete Optimization, 2011).
In this paper, we give an improved kernel of O(k^3) vertices for Diamond-free Edge Deletion. We give an alternative proof of the NP-completeness of the problem and observe that it cannot be solved in time 2^{o(k)} * n^{O(1)}, unless the Exponential Time Hypothesis fails.
@InProceedings{sandeep_et_al:LIPIcs.IPEC.2015.365,
author = {Sandeep, R. B. and Sivadasan, Naveen},
title = {{Parameterized Lower Bound and Improved Kernel for Diamond-free Edge Deletion}},
booktitle = {10th International Symposium on Parameterized and Exact Computation (IPEC 2015)},
pages = {365--376},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-939897-92-7},
ISSN = {1868-8969},
year = {2015},
volume = {43},
editor = {Husfeldt, Thore and Kanj, Iyad},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.IPEC.2015.365},
URN = {urn:nbn:de:0030-drops-55976},
doi = {10.4230/LIPIcs.IPEC.2015.365},
annote = {Keywords: edge deletion problems, polynomial kernelization}
}