空集
空集者，無物之集也。夫集，集數物於一耳。至若斯集，凡集合者，咸括之耳。泰西記之曰「 } 」、「∅」。造此符者，布爾巴基也。布爾巴基者，法蘭西群疇自謂也。
空集公理曰：「空集存也」。外延公理曰：「二集物咸同者，同也」。故無物之集皆同也。
空集一文似未成。宜善之。This article uses material from the Wikipedia 古文 / 文言文 article 空集, which is released under the Creative Commons Attribution-ShareAlike 3.0 license ("CC BY-SA 3.0"); additional terms may apply (view authors). 若無側注，諸文皆奉CC BY-SA 4.0以行。 Images, videos and audio are available under their respective licenses.
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