Online Ramsey Theory for Planar Graphs

Šárka Petříčková


An online Ramsey game $(G,\mathcal{H})$ is a game between Builder and Painter, alternating in turns. During each turn, Builder draws an edge, and Painter colors it blue or red. Builder's goal is to force Painter to create a monochromatic copy of $G$, while Painter's goal is to prevent this. The only limitation for Builder is that after each of his moves, the resulting graph has to belong to the class of graphs $\mathcal{H}$. It was conjectured by Grytczuk, Hałuszczak, and Kierstead (2004) that if $\mathcal{H}$ is the class of planar graphs, then Builder can force a monochromatic copy of a planar graph $G$ if and only if $G$ is outerplanar. Here we show that the "only if" part does not hold while the "if" part does.


Ramsey theory; Online Ramsey games; Planar graphs; Outerplanar graphs; Game theory; Builder and Painter

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