Spherical geometry other geometric concepts are defined as in plane geometry, but with straight lines replaced by great circles. Thus, in spherical geometry, angles are defined between great circles, resulting in a spherical trigonometry that differs from ordinary trigonometry in many respects; for example, the sum of the interior angles of a triangle exceeds 180 degrees. Spherical geometry is "not" elliptic geometry, but is rather a "subset" of elliptic geometry. For example, it shares with that geometry the property that a line has no parallels through a given point. Contrast this with Euclidean geometry, in which a line has one parallel through
Six Degrees: The Science of a Connected Age Six Degrees: The Science of a Connected Age Six Degrees: The Science of a Connected Age (2004 in paperback, and 2003 in hardcover, ) is a popular science book by Duncan J. Watts covering the application of network theory to sociology. The book covers Watts' own work on small-world networks, and continues on to cover scale-free networks, network searching, epidemics and network failures, social decision making, thresholds in networks, and innovation in large organizations and its lack. In addition to covering the theoretical models and empirical case studies, the book also includes several stories about the character of the researchers