Occurs check

实例化的变量，因此在效果上变成了它的别名。在很多现代 Prolog 方言和一阶逻辑演算中，变量不能合一于包含它的项；这叫做出现检查（英语：Occurs check）。 Prolog 原子只能合一于同一个原子。 类似的，项只能合一于另一个项，如果顶部函数符号和项的元数(arity)和这个项是一样的，并且参数可以同时合一。注意这是递归行为。

Campos. Lo que la lluvia regala a Yoro (discusses a rain of fishes that occurs annually in Honduras). Hablemos. 2004-11-07. （原始内容存档于2012-04-02）.  Comptes

dispersal distance（英语：Marine larval ecology） of any marine invertebrate which occurs along the west coast of North America. A 螺殼 of Monoplex parthenopeus with

the child who smiles or even laughs when being chastised." Flop: "Flop occurs if, and when, the freeze mechanism fails.... The survival purpose of the

folding problem—understanding in detail how the folding process actually occurs in nature (and how sometimes they can also misfold). But even with such