Wow, is this fun: a graph theory-based game called Planarity.
Given a set of vertices and edges, your job is to untangle the graph so that no two edges intersect. In essence, you are proving that the given graph is indeed a planar graph.
If it takes you a long time to succeed, just tell your friends you got caught up thinking about questions like “How can I prove it’s always possible to untangle this graph?” and “I wonder how many more edges I could add while keeping this puzzle solvable?” That’s what I tell people.
