empty set

音标发音

Start from scratch: Start with an empty set of conditions and add your own.
从头开始：从一组空的条件开始并添加您自己的条件。
This occurs because the fields are empty, so we are actually multiplying nothing by nothing (or empty set by empty set).
之所以会出现这个问题是由于字段是空的，因此实际上进行的计算是零乘零（或者空集乘空集）。
When you invoke a Groovy method that has no parameters, you must call it with an empty set of parentheses, which allows Groovy to distinguish between a property access from a method call.
当您调用一个没有参数的 Groovy 方法时，您必须使用一对空括号调用它，这使得 Groovy 可以分清一个属性访问和一个方法调用之间的区别。

Picture this: a stately room full of empty chairs set up two rows deep in a semi circle.
FORBES: Women Politicians And Twitter Train Wrecks
As soon as Munin bullied him, he headed over to a set of empty containers, prised the lids off them enthusiastically, and pretended to eat.
ECONOMIST: Now, it seems, even the bird-brained have theories of mind

a set (= a group of numbers) that contains no elements, represented by the symbol {}