15 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] |
| 18529 | Relations are expressed either as absolute facts, or by a relational concept [William of Ockham] |
| 16779 | Cut wood doesn't make a new substance, but seems to make separate subjects [William of Ockham] |
| 16757 | Hot water naturally cools down, which is due to the substantial form of the water [William of Ockham] |
| 9102 | If an animal approached from a distance, we might abstract 'animal' from one instance [William of Ockham] |
| 9114 | There are no secure foundations to prove the separate existence of mind, in reason or experience [William of Ockham] |
| 1590 | The just man does not harm his enemies, but benefits everyone [Plato] |
| 9115 | To love God means to love whatever God wills to be loved [William of Ockham] |