12 ideas
| 291 | Don't assume that wisdom is the automatic consequence of old age [Plato] |
| 22026 | Philosophy is homesickness - the urge to be at home everywhere [Novalis] |
| 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] |
| 19591 | Desire for perfection is an illness, if it turns against what is imperfect [Novalis] |
| 293 | Being unafraid (perhaps through ignorance) and being brave are two different things [Plato] |