What's the name of this graph?
I saw this special graph is used in graph theory for a counterexample of several statements.
But I don't remember the name of this graph.
Could you help me?
Thanks.
This is the Grötzsch graph see for example here. It is named after German mathematician Herbert Grötzsch. The Grötzsch graph is the smallest triangle-free graph with $11$ vertices and chromatic number $4$.