The Penrose triangle, also known as the impossible tribar is an icon for cohomology.  It is literally the icon for Cech cohomology on Wikipedia.  The idea goes back to a paper by Roger Penrose in 1992, but was first reported by Penrose several years earlier.  There, he shows how the impossibility of the figure depends…

Self-duality equations in gauge theory can be complexified in many inequivalent ways, but there are two obvious options: One can extend Hodge duality in either a complex linear fashion, or in a conjugate linear one. In general, the two cases result in two very different equations. The first case was first studied by Haydys, while…