15 ideas
| 13201 | ∈ says the whole set is in the other; ⊆ says the members of the subset are in the other [Enderton] |
| 13206 | A 'linear or total ordering' must be transitive and satisfy trichotomy [Enderton] |
| 13204 | The 'ordered pair' <x,y> is defined to be {{x}, {x,y}} [Enderton] |
| 13200 | Note that {Φ} =/= Φ, because Φ ∈ {Φ} but Φ ∉ Φ [Enderton] |
| 13199 | The empty set may look pointless, but many sets can be constructed from it [Enderton] |
| 13203 | The singleton is defined using the pairing axiom (as {x,x}) [Enderton] |
| 13202 | Fraenkel added Replacement, to give a theory of ordinal numbers [Enderton] |
| 13205 | We can only define functions if Choice tells us which items are involved [Enderton] |
| 9390 | Logic guides thinking, but it isn't a substitute for it [Rumfitt] |
| 9389 | Vague membership of sets is possible if the set is defined by its concept, not its members [Rumfitt] |
| 7257 | All modern social systems seem to be conspiracies of the rich [More,T] |
| 7254 | If you try to get elected, you should be permanently barred from seeking office [More,T] |
| 7255 | Only Utopians fail to see glory in warfare [More,T] |
| 7253 | In Utopia, legal euthanasia is considered honourable [More,T] |
| 7256 | In Utopia, the Supreme Being is identical with Nature [More,T] |