Predicate functions are often very simple and better off being defined using a closure.
对函数使用断言通常很简单，而且最好使用闭包定义。
2
RDF documents are made up of simple statements that consist of three parts each: the subject, the predicate, and the object (value).
RDF文档由一些简单的语句组成，每个语句包含三个部分：主语、谓语和宾语(值)。
3
Finding all the weblogs mentioned in the list is a simple matter of calling the blogs method, which performs a query for all the objects of statements with foaf: weblog as their predicate.