关于一个定义的解释，请求帮忙！

skysophie

Definitions.-An arrangement of v objects (called treatments) in b sets
(called blocks) will be called a pairwise balanced design of index unity and type
+ e# U) q4 L' e! I2 f, b% r9 V* H(v; ki, k2, .. ., ki) if each block contains either k1, k2, .. ., or km treatments which
are all distinct (k, < v, k, $ kj), and every pair of distinct treatments occurs exactly
in one block of the design. If the number of blocks containing k, treatments is
b,, then clearly  b = A bi, v(v-1) = i biki(k -1)。。。

2 ^1 x( ?% p1 i* B5 c谁能帮我解释一下，可以举个简单的例子。。谢谢！~
. n9 ]- U" y3 E1 h! `0 v; E

角凳

是告诉我们这是哪个领域的么？？