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
5 X+ r4 q1 g7 K$ N0 W(called blocks) will be called a pairwise balanced design of index unity and type
(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
* b# }6 W6 q0 X% T, p' ~7 Ain one block of the design. If the number of blocks containing k, treatments is
0 b; E5 T/ a& @, \- m7 e& [+ _- i4 Zb,, then clearly  b = A bi, v(v-1) = i biki(k -1)。。。

谁能帮我解释一下，可以举个简单的例子。。谢谢！~
. L; D8 {% S( E/ W- C

角凳

是告诉我们这是哪个领域的么？？