\begin{definition}[Definition:Block Incidence Matrix of a Design]
The '''block incidence matrix''' of a $\tuple {v, b, r, k, \lambda}$-BIBD, is a $v \times b$ incidence matrix $A = \sqbrk {a_{ij} }$ such that:
:$a_{ij} = \begin {cases}
1 & : \text {if the $i$th point is in the $j$th block} \\
0 & : \text {otherwise}
\end {cases}$
Category:Definitions/Design Theory
\end{definition}