🚧良序╱well ordering

良序性╱🚧 under construction -> ordered set, smallest element

集合 ⟩ 關係 ⟩ 二元 ⟩ well ordering

An ordered set $S$ is said to be well-ordered if each and every nonempty subset has a smallest (or least) element.

$\forall A \subseteq S, \ A \neq \empty, \ \exists m \in A \ \ni \forall x \in A, \ m \le x$

📗 參考

• Brilliant ⟩ The Well-ordering Principle

👥 相關

• 自然數的良序性