Solitons: Differential equations, symmetries, and infinite-dimensional algebras
《Solitons: Differential equations, symmetries, and infinite-dimensional algebras》 · 第 112 页 · Section 4.12「Projective Space」
For every scheme $S$ we define $\mathbb P^n_S=\mathbb P^n_{\mathbb Z}\times_{\mathbb Z}S$ and call this $S$-scheme the projective space of relative dimension $n$ over $S$.