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Another example is a block design. Here X is a finite set of "points" and Y is a class of subsets of X, called "blocks", subject to rules that depend on the type of design. The incidence matrix is an important tool in the theory of block designs. For instance, it can be used to prove Fisher's inequality, a fundamental theorem of balanced incomplete 2-designs (BIBDs), that the number of blocks is at least the number of points. Considering the blocks as a system of sets, the permanent of the incidence matrix is the number of systems of distinct representatives (SDRs).

Another example is a block design. Here X is a finite set of "points" and Y is a class of subsets of X, called "blocks", subject to rules that depend on the type of design. The incidence matrix is an important tool in the theory of block designs. For instance, it can be used to prove Fisher's inequality, a fundamental theorem of balanced incomplete 2-designs (BIBDs), that the number of blocks is at least the number of points. Considering the blocks as a system of sets, the permanent of the incidence matrix is the number of systems of distinct representatives (SDRs).

另一个例子是块设计。这里''X''是一个有限的“点”集合，而''Y'' 是''x''的一类子集，称为“块” ，受依赖于设计类型的规则的制约。关联矩阵是块设计理论中的一个重要工具。例如，它可以用来证明'''<font color="#ff8000">Fisher不等式 Fisher's inequality</font>'''，一个平衡不完全2- 设计(BIBDs)的基本定理，块的数目至少是点的数目。将块看作一个集合系统，关联矩阵的常数是不同代表系统的个数（SDRs）。

另一个例子是块设计。这里 ''X'' 是一个有限的“点”集合，而 ''Y'' 是 ''X'' 的一类子集，称为“块” ，受依赖于设计类型的规则的制约。关联矩阵是块设计理论中的一个重要工具。例如，它可以用来证明'''<font color="#ff8000">Fisher不等式 Fisher's inequality</font>'''，一个平衡不完全2- 设计(BIBDs)的基本定理，块的数目至少是点的数目。将块看作一个集合系统，关联矩阵的常数是不同代表系统的个数（SDRs）。

==References==

==References==