一句话：给出在 n 枚硬币中用天平以最少保证称量次数找出可能存在的假币并判定其轻重的方案。
本文研究经典的天平假币问题：有 n 枚外观相同的硬币，其中可能有一枚假币；若假币存在，它比真币轻或重，但事先不知道是轻是重，也不知道轻重程度。给定一架无砝码的双盘天平，每次可在两盘放置相同数量的硬币进行称量，结果有三种：左盘轻、平衡或左盘重。论文的目标是设计一种称量方案（recipe），使得在最坏情况下保证用最少的称量次数确定假币是否存在，并在存在时判断其是轻还是重。该问题属于组合搜索与决策树优化，要求方案对所有可能情形都有效。
There are n coins, all identical in appearance, one of which may be fake. The fake coin, if it exists, is either lighter or heavier than the fair coins, but it is not known which, nor by how much. Given is a balance with two pans but no weights. Equal number of coins can be placed on each pan and weighed. There are three possible outcomes: the left-hand pan may be lighter than the right-hand pan, or of equal weight, or heavier. Design a recipe for determining the minimum number of weighings guaranteed to determine the fake coin, if it exists, and whether it is lighter or heavier than the others.