文摘
We investigate the function LH(n)=max{|H∩P(A)|:|A|=n} where H is a set of finite subsets of λ such that every λ-sized subset of λ has arbitrarily large subsets form H. For κ=ℵ1, limLH(n)/n→∞ and 03" class="mathmlsrc">03.gif&_user=111111111&_pii=S0168007216300690&_rdoc=1&_issn=01680072&md5=d2f40d99f41eae016e79411c55355ca7" title="Click to view the MathML source">LH(n)=O(n2), and in different models of set theory, either bound can be sharp. If λ>ℵ1, LH(n)>cn2 for some e05e4952b838b1cd884b652" title="Click to view the MathML source">c>0 and n sufficiently large. If λ is strong limit singular, then 3ed3902546c11" title="Click to view the MathML source">LH is superpolynomial. If κ<λ are uncountable cardinals, we call a family Hκ-dense (strongly κ-dense) in λ if every κ-sized subset of λ contains a set (arbitrarily large sets) in H. We show under GCH that if H is κ+-dense in κ+r (r finite), then LH(n)/nr→∞ (κ=ω) and e0527be9d98aa141d5b19e" title="Click to view the MathML source">LH(n)>cnr+1 (κ>ω). We also give bounds for LH(n) when H has large chromatic or coloring number.