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] |
| 9758 | To make sense of personal identity, focus on agency rather than experience [Korsgaard] |
| 9757 | A person viewed as an agent makes no sense without its own future [Korsgaard] |
| 9759 | Theory of action focuses on explanation and prediction; practical action on justification and choice [Korsgaard] |
| 9760 | Self-concern may be a source of pain, or a lack of self-respect, or a failure of responsibility [Korsgaard] |
| 9761 | Personal concern for one's own self widens out into concern for the impersonal [Korsgaard] |
| 13304 | Learned men gain more in one day than others do in a lifetime [Posidonius] |
| 20820 | Time is an interval of motion, or the measure of speed [Posidonius, by Stobaeus] |