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Published online by Cambridge University Press: 24 October 2008
For cardinal numbers λ, K, ∑ a (λ, K)-family is a family of sets such that |
| =
and |A| = K for every A ε
, and a (λ, K, ∑)-family is a (λ,K)-family
such that |∪
| = ∑. Two sets A, B are said to be almost disjoint if
and an almost disjoint family of sets is a family whose members are pairwise almost disjoint. A representing set of a family is a set X ⊆ ∪
such that X ∩ A = ⊘ for each A ε
. If
is a family of sets and |∪
| = ∑, then we write
εADR(
) to signify that
is an almost disjoint family of ∑-sized representing sets of
. Also, we define a cardinal number