14 ideas
| 13201 | ∈ says the whole set is in the other; ⊆ says the members of the subset are in the other [Enderton] |
| 13204 | The 'ordered pair' <x,y> is defined to be {{x}, {x,y}} [Enderton] |
| 13206 | A 'linear or total ordering' must be transitive and satisfy trichotomy [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] |
| 23476 | Logical constants seem to be entities in propositions, but are actually pure form [Russell] |
| 23477 | We use logical notions, so they must be objects - but I don't know what they really are [Russell] |
| 18273 | Logical truths are known by their extreme generality [Russell] |
| 22315 | There can't be a negative of a complex, which is negated by its non-existence [Potter on Russell] |
| 14961 | Clearly a pipe can survive being taken apart [Cartwright,R] |
| 14962 | Bodies don't becomes scattered by losing small or minor parts [Cartwright,R] |