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==History of set theory==

==History of set theory==

It was developed in the late 1800s, primarly by the German mathematician [[Georg Cantor]].  This initial attempt became known as "naive set theory" because mathematicians found flaws in it. It was replaced by "axiomatic set theory" in the early 1900s. The most commonly used such axiomatization is [[Zermelo-Fraenkel]] set theory.

It was developed in the late 1800s, primarily by the German mathematician [[Georg Cantor]].  This initial attempt became known as "naive set theory" because mathematicians found flaws in it. It was replaced by "axiomatic set theory" in the early 1900s. The most commonly used such axiomatization is [[Zermelo-Fraenkel]] set theory.

An initial insight of set theory, against intense opposition by established mathematicians, was that some infinities are larger than others.  Previously it was thought that infinity had only one size.

An initial insight of set theory, against intense opposition by established mathematicians, was that some infinities are larger than others.  Previously it was thought that infinity had only one size.