In mathematics topological graph theory is a branch of graph theory. It studies the embedding of graphs in surfaces.
Embedding a graph in a surface means we want to draw the graph on a surface, a sphere for example, without two edges intersecting. A basic embedding problem often presented as a mathematical puzzle is the three cottage problem. More important applications can be found in printing electronic circuits where the aim is to print (embed) a circuit (the graph) on a circuit board (the surface) without two connections crossing each other and resulting in a short circuit.
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