In the following electrical circuit the textbook says it is non-planar. I was curious from a mathematics perspective on how to approach this and found Kuratowski's Theorem about having a K5 or K3,3 subgraph if it is non-planar. Can someone point out where the K3,3 subgraph is in this diagram? I am assuming it's not K5 since there are not 4 edges between each node. Also note for electrical circuits there is a node between each element. I am unsure whether the nodes in electrical circuits and the vertices in graph theory are equivalent