Solitons: Differential equations, symmetries, and infinite-dimensional algebras
《Solitons: Differential equations, symmetries, and infinite-dimensional algebras》 · 第 99 页 · Definition 4.10
For two morphisms $f:X\to S$ and $g:Y\to S$ in $\mathcal C$, a triple $(Z,p,q)$ with $f\circ p=g\circ q$ is called a fiber product of $X$ and $Y$ over $S$ if for every object $T$ and every pair $u:T\to X$, $v:T\to Y$ with $f\circ u=g\circ v$, there exists a unique $w:T\to Z$ such that $p\circ w=u$ and $q\circ w=v$.