13 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] |
| 9295 | Not only substances have attributes; events, actions, states and qualities can have them [Teichmann] |
| 9293 | Body-spirit interaction ought to result in losses and increases of energy in the material world [Teichmann] |
| 468 | Musical performance can reveal a range of virtues [Damon of Ath.] |
| 9292 | The Soul has no particular capacity (in the way thinking belongs to the mind) [Teichmann] |
| 9294 | No individuating marks distinguish between Souls [Teichmann] |