标题： 关于闭算子亏数乘积公式的几点注记 显示英文标题

标题： Some Remarks on the Product Formula for Defect Numbers of Closed Operators

摘要： 这篇主要具有教学性质的论文回顾了利用半-Fredholm 算子理论的结果，关于闭算子乘积的亏指数的一些事实，然后将这些事实应用于对称算子的正整数次幂，继而应用于某些极小阶的 Sturm-Liouville 算子和极小高偶阶常微分及偏微分算子。 我们还指出，在比较不同研究小组在这个课题上的工作时，一些意外的遗漏机会。 显示英文摘要

摘要： This largely pedagogical paper recalls some facts on defect numbers of products of closed operators employing results from the theory of semi-Fredholm operators and then applies these facts to positive integer powers of symmetric operators and subsequently to certain minimal Sturm--Liouville and minimal higher even-order ordinary and partial differential operators. We also point out some unexpected missed opportunities when comparing the work of different groups on this subject.