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
% S  J8 J4 F( H  O# E  e(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
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)。。。
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( k, Y: S& o' _谁能帮我解释一下，可以举个简单的例子。。谢谢！~
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角凳

是告诉我们这是哪个领域的么？？