Complex sentence: For instance, the complete graph is not planar but can be embedded onto a torus, with each face of the embedding being a triangle; it has the Heawood graph as its dual graph.
Split into simpler sentences: For instance, the complete graph is a toroidal graph: it is not planar but can be embedded onto a torus, with each face of the embedding being a triangle. This embedding has the Heawood graph as its dual graph.