Stratum is an important idea of three dimension strata model. It plays a key action in instauration of three dimension strata model.

地层作为三维地层模型的一个重要概念，在三维地层模型的建立中起着关键作用。

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These layers are called strata and a single layer is called a stratum.

这些岩层被称作地层（strata）（stratum的复数形式）， 单个岩层称为stratum。

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It seems that mathematical ideas are arranged somehow in strata, the ideas in each stratum being linked by a complex of relations both among themselves and with those above and below.

数学观念似乎以层级的方式排列的，每一层的观念以复杂的关系与同层的和上下层的观念相联系。

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