Definition:Projective Algebraic Set

Definition
Let $K$ be a field.

Let $n \in \N_{>0}$.

Let $\map {\mathbb P^n} K$ be the $n$-projective space.

Let $S = K \sqbrk {X_0, \ldots, X_n}$ be the ring of polynomial functions in $n + 1$ variables over $K$.

Then a subset $X \subseteq \map {\mathbb P^n} K$ is a projective algebraic set :
 * there is a subset $T \subseteq S$ of homogeneous elements such that:
 * $\ds X = \bigcap_{f \mathop \in T} \set { \struct {x_0 : \cdots : x_n} \in \map {\mathbb P^n} K : \map f {x_0, \ldots, x_n}  =0 }$

Also see

 * Definition:Affine Algebraic Set