for all } and }. More generally, this definition makes sense in cones in }. A set } is called a cone if, whenever , then for all }; that is, a subset is a cone if it contains the complex line through each of its points. If is an open set (in either the analytic topology or the Zariski topology), let } be the cone over "U": the preimage of "U" under the projection . Finally, for each integer "k", let "O"("k")("U") be the set of functions that are homogeneous of degree "k" in "V". This defines a sheaf of sections of a certain line bundle, denoted by "O"("k").