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arXiv 1012.0557cs.DScs.DMmath.PR
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Lovasz局部引理的无限可计算版本

Infinite computable version of Lovasz Local Lemma

Andrey Rumyantsev

摘要:

Lovász局部引理(LLL)是一个概率工具,它允许我们在标准概率论证不起作用的情况下(有许多部分独立的条件)证明组合对象的存在性。LLL也可以用来证明一个无限条件集的一致性,使用标准的紧致性参数(如果一个无限条件集是不一致的,那么它的某些有限部分也是不一致的,这与LLL相矛盾)。用这种方法,我们证明了满足所有条件的对象确实存在(尽管这个事件的概率等于~ $0$)。然而,如果我们有兴趣找到一个满足所有约束的可计算解,紧性参数就不再起作用了。Moser和Tardos最近给出了LLL的一个很好的建设性证明。兰斯Fortnow问是否可以应用Moser-Tardos技术来证明存在一个可计算的解决方案。我们证明了这确实是可能的(在几乎与非建设性版本中使用的相同条件下)。

英文摘要:

Lovász Local Lemma (LLL) is a probabilistic tool that allows us to prove the existence of combinatorial objects in the cases when standard probabilistic argument does not work (there are many partly independent conditions). LLL can be also used to prove the consistency of an infinite set of conditions, using standard compactness argument (if an infinite set of conditions is inconsistent, then some finite part of it is inconsistent, too, which contradicts LLL). In this way we show that objects satisfying all the conditions do exist (though the probability of this event equals~$0$). However, if we are interested in finding a computable solution that satisfies all the constraints, compactness arguments do not work anymore. Moser and Tardos recently gave a nice constructive proof of LLL. Lance Fortnow asked whether one can apply Moser--Tardos technique to prove the existence of a computable solution. We show that this is indeed possible (under almost the same conditions as used in the non-constructive version).

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