5 ideas
17833 | The first-order ZF axiomatisation is highly non-categorical [Hallett,M] |
17834 | Non-categoricity reveals a sort of incompleteness, with sets existing that the axioms don't reveal [Hallett,M] |
17837 | Zermelo allows ur-elements, to enable the widespread application of set-theory [Hallett,M] |
17836 | The General Continuum Hypothesis and its negation are both consistent with ZF [Hallett,M] |
8249 | Class membership is not transitive, unlike being part of a part of the whole [Lesniewski, by George/Van Evra] |