AxiomAxiomatic theoriesAxiomatic set theory was developed in response to these early attempts to understand sets, with the goal of determining precisely what operations were allowed and when.
TheoremCantor's TheoremIntermediateFor any set AAA, the set of all subsets of AAA (the power set of AAA) has a strictly greater cardinality than AAA itself.\n∣P(A)∣>∣A∣|P(A)| > |A|∣P(A)∣>∣A∣
DefinitionNaïve Set Theory (Definition)Sets are defined by a property P(x)P(x)P(x), i.e., S={x∣P(x)}S = \{x \mid P(x)\}S={x∣P(x)}. This allows for Russell's Paradox.