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*考拉兹猜想（英语：Collatz conjecture），又称为奇偶归一猜想、3n+1猜想、冰雹猜想、角谷猜想、哈塞猜想、乌拉姆猜想或叙拉古猜想，是指对于每一个正整数，如果它是奇数，则对它乘3再加1，如果它是偶数，则对它除以2，如此循环，最终都能够得到1。

*考拉兹猜想（英语：Collatz conjecture），又称为奇偶归一猜想、3n+1猜想、冰雹猜想、角谷猜想、哈塞猜想、乌拉姆猜想或叙拉古猜想，是指对于每一个正整数，如果它是奇数，则对它乘3再加1，如果它是偶数，则对它除以2，如此循环，最终都能够得到1。

*分形（英语：fractal，源自拉丁语：frāctus，有“零碎”、“破裂”之意），又称碎形、残形，通常被定义为“一个粗糙或零碎的几何形状，可以分成数个部分，且每一部分都（至少近似地）是整体缩小后的形状”，即具有自相似的性质。 分形在数学中是一种抽象的物体，用于描述自然界中存在的事物。人工分形通常在放大后能展现出相似的形状。 分形也被称为扩展对称或展开对称。如果在每次放大后，形状的重复是完全相同的，这被称为自相似。

*分形（英语：fractal，源自拉丁语：frāctus，有“零碎”、“破裂”之意），又称碎形、残形，通常被定义为“一个粗糙或零碎的几何形状，可以分成数个部分，且每一部分都（至少近似地）是整体缩小后的形状”，即具有自相似的性质。 分形在数学中是一种抽象的物体，用于描述自然界中存在的事物。人工分形通常在放大后能展现出相似的形状。 分形也被称为扩展对称或展开对称。如果在每次放大后，形状的重复是完全相同的，这被称为自相似。分形与其他几何图形相似但又有所不同。当你缩放一个图形时，你就能看出分形和其他几何图形的区别。将一个多边形的边长加倍，它的面积变为原来的四倍。新的边长与旧边长相比增加了 2 倍，而面积增加了 4 倍。平面内的多边形在二维空间中，指数 2 刚好是多边形所在的二维空间的维数。类似的，对于三维空间中的球，如果它的半径加倍，则它的体积变为原来的 8 倍，指数 3 依旧是球所在空间的维数。如果将分形的一维长度加倍，此时不一定是以整数的幂进行缩放。

分形与其他几何图形相似但又有所不同。当你缩放一个图形时，你就能看出分形和其他几何图形的区别。将一个多边形的边长加倍，它的面积变为原来的四倍。新的边长与旧边长相比增加了 2 倍，而面积增加了 4 倍。平面内的多边形在二维空间中，指数 2 刚好是多边形所在的二维空间的维数。类似的，对于三维空间中的球，如果它的半径加倍，则它的体积变为原来的 8 倍，指数 3 依旧是球所在空间的维数。如果将分形的一维长度加倍，此时不一定是以整数的幂进行缩放。

*同构（英语：isomorphism）指的是一个保持结构的双射。在更一般的范畴论语言中，同构指的是一个态射，且存在另一个态射，使得两者的复合是一个恒等态射。

*同构（英语：isomorphism）指的是一个保持结构的双射。在更一般的范畴论语言中，同构指的是一个态射，且存在另一个态射，使得两者的复合是一个恒等态射。正式的表述是：同构是在数学对象之间定义的一类映射，它能揭示出在这些对象的属性或者操作之间存在的关系。若两个数学结构之间存在同构映射，那么这两个结构叫做是同构的。一般来说，如果忽略掉同构的对象的属性或操作的具体定义，单从结构上讲，同构的对象是完全等价的。

*元定理（metatheorem）A notable early citation is Quine's 1937 use of the word "metatheorem",[6] where meta- has the modern meaning of "an X about X". (Note earlier uses of "meta-economics" and even "metaphysics" do not have this doubled conceptual structure – they are about or beyond X but they do not themselves constitute an X).Douglas Hofstadter, in his 1979 book Gödel, Escher, Bach (and in the sequel, Metamagical Themas), popularized this meaning of the term. The book, which deals with self-reference and strange loops, and touches on Quine and his work, was influential in many computer-related subcultures and may be responsible for the popularity of the prefix, for its use as a solo term, and for the many recent coinages which use it.[7] Hofstadter uses meta as a stand-alone word, as an adjective and as a directional preposition ("going meta," a term he coins for the old rhetorical trick of taking a debate or analysis to another level of abstraction, as when somebody says "This debate isn't going anywhere"). This book may also be responsible for the association of "meta" with strange loops, as opposed to just abstraction.[citation needed] The sentence "This sentence contains thirty-six letters," and the sentence which embeds it, are examples of "metasentences" referencing themselves in this way.

*元定理（metatheorem）A notable early citation is Quine's 1937 use of the word "metatheorem",[6] where meta- has the modern meaning of "an X about X". (Note earlier uses of "meta-economics" and even "metaphysics" do not have this doubled conceptual structure – they are about or beyond X but they do not themselves constitute an X).Douglas Hofstadter, in his 1979 book Gödel, Escher, Bach (and in the sequel, Metamagical Themas), popularized this meaning of the term. The book, which deals with self-reference and strange loops, and touches on Quine and his work, was influential in many computer-related subcultures and may be responsible for the popularity of the prefix, for its use as a solo term, and for the many recent coinages which use it.[7] Hofstadter uses meta as a stand-alone word, as an adjective and as a directional preposition ("going meta," a term he coins for the old rhetorical trick of taking a debate or analysis to another level of abstraction, as when somebody says "This debate isn't going anywhere"). This book may also be responsible for the association of "meta" with strange loops, as opposed to just abstraction.[citation needed] The sentence "This sentence contains thirty-six letters," and the sentence which embeds it, are examples of "metasentences" referencing themselves in this way.