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Simple games versus weighted voting games.

Hof, F. and Kern, W. and Kurz, S. and Paulusma, D. (2018) 'Simple games versus weighted voting games.', in Algorithmic game theory : 11th International Symposium, SAGT 2018, Beijing, China, September 11-14, 2018, Proceedings. Cham: Springer, pp. 69-81. Lecture notes in computer science. (11059).


A simple game (N, v) is given by a set N of n players and a partition of 2N into a set L of losing coalitions L with value v(L)=0 that is closed under taking subsets and a set W of winning coalitions W with v(W)=1 . Simple games with α=minp≥0maxW∈W,L∈Lp(L)p(W)<1 are exactly the weighted voting games. Freixas and Kurz (IJGT, 2014) conjectured that α≤14n for every simple game (N, v). We confirm this conjecture for two complementary cases, namely when all minimal winning coalitions have size 3 and when no minimal winning coalition has size 3. As a general bound we prove that α≤27n for every simple game (N, v). For complete simple games, Freixas and Kurz conjectured that α=O(n−−√) . We prove this conjecture up to a lnn factor. We also prove that for graphic simple games, that is, simple games in which every minimal winning coalition has size 2, computing α is NP-hard, but polynomial-time solvable if the underlying graph is bipartite. Moreover, we show that for every graphic simple game, deciding if α<a is polynomial-time solvable for every fixed a>0 .

Item Type:Book chapter
Full text:(AM) Accepted Manuscript
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Publisher statement:The final publication is available at Springer via
Date accepted:05 July 2018
Date deposited:31 July 2018
Date of first online publication:27 August 2018
Date first made open access:No date available

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