Genus-2 surface. A genus-2 surface.
In mathematics, a genus-2 surface (also known as a double torus or two-holed torus) is a surface formed by the connected sum of two tori. That is to say, from each of two tori the interior of a disk is removed, and the boundaries of the two disks are identified (glued together), forming a double torus. Double torus knots are studied in knot theory. Example[edit] Torus. A torus In geometry, a torus (pl. tori) is a surface of revolution generated by revolving a circle in three-dimensional space about an axis coplanar with the circle.
If the axis of revolution does not touch the circle, the surface has a ring shape and is called a ring torus or simply torus if the ring shape is implicit. In topology, a ring torus is homeomorphic to the Cartesian product of two circles: S1 × S1, and the latter is taken to be the definition in that context. The History Of Zero. From placeholder to the driver of calculus, zero has crossed the greatest minds and most diverse borders since it was born many centuries ago.
Today, zero is perhaps the most pervasive global symbol known. In the story of zero, something can be made out of nothing. Zero, zip, zilch - how often has a question been answered by one of these words? Countless, no doubt. Binary.