In Riemannian geometry, the sectional curvature is one of the ways to describe the curvature of Riemannian manifolds. The sectional curvature K(σp) depends on a two-dimensional plane σp in the tangent space at p. It is the Gaussian curvature of the surface which has the plane σp as a tangent plane at p, obtained from geodesics which start at p in the directions of σp (in other words, the image of σp under the exponential map at p). The sectional curvature is a smooth real-valued function on the 2-Grassmannian bundle over the manifold.
The sectional curvature determines the curvature tensor completely...
Female (♀) is the sex of an organism, or a part of an organism, that produces non-mobile ova (egg cells). Most female mammals, including female humans, have two X chromosomes.
== Defining characteristics ==
The ova are defined as the larger gametes in a heterogamous reproduction system, while the smaller, usually motile gamete, the spermatozoon, is produced by the male. A female individual cannot reproduce sexually without access to the gametes of a male (an exception is parthenogenesis). Some organisms can reproduce both sexually and asexually.
There is no single genetic mechanism behind...
