The Relative Signed Clique Number of Planar Graphs is 8

  • Sandip Das
  • Soumen NandiEmail author
  • Sagnik Sen
  • Ritesh Seth
Conference paper
Part of the Lecture Notes in Computer Science book series (LNCS, volume 11394)


A simple signed graph \((G, \varSigma )\) is a simple graph with a \(+\)ve or a −ve sign assigned to each of its edges where \(\varSigma \) denotes the set of −ve edges. A cycle is unbalanced if it has an odd number of −ve edges. A vertex subset R of \((G, \varSigma )\) is a relative signed clique if each pair of non-adjacent vertices of R is part of an unbalanced 4-cycle. The relative signed clique number \(\omega _{rs}((G, \varSigma ))\) of \((G,\varSigma )\) is the maximum value of |R| where R is a relative signed clique of \((G,\varSigma )\). Given a family \(\mathcal {F}\) of signed graphs, the relative signed clique number is \(\omega _{rs}(\mathcal {F}) = \max \{\omega _{rs}((G,\varSigma ))|(G,\varSigma ) \in \mathcal {F}\}\). For the family \(\mathcal {P}_3\) of signed planar graphs, the problem of finding the value of \(\omega _{rs}(\mathcal {P}_3)\) is an open problem. In this article, we close it by proving \(\omega _{rs}(\mathcal {P}_3)=8\).


Signed graphs Relative clique number Planar graphs 


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Copyright information

© Springer Nature Switzerland AG 2019

Authors and Affiliations

  • Sandip Das
    • 1
  • Soumen Nandi
    • 2
    Email author
  • Sagnik Sen
    • 3
  • Ritesh Seth
    • 3
  1. 1.Indian Statistical InstituteKolkataIndia
  2. 2.Birla Institute of Technology and Science Pilani, Hyderabad CampusPilaniIndia
  3. 3.Ramakrishna Mission Vivekananda Educational and Research InstituteKolkataIndia

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