20 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] |
| 19400 | Possibles demand existence, so as many of them as possible must actually exist [Leibniz] |
| 19401 | God's sufficient reason for choosing reality is in the fitness or perfection of possibilities [Leibniz] |
| 19402 | The actual universe is the richest composite of what is possible [Leibniz] |
| 23429 | The environment needs localised politics, with its care for the land [Dobson] |
| 23424 | An ideology judges things now, and offers an ideal, with a strategy for reaching it [Dobson] |
| 23426 | Ecologism is often non-liberal, by claiming to know other people's best interests [Dobson] |
| 23427 | Socialism can be productive and centralised, or less productive and decentralised [Dobson] |
| 23428 | Difference feminists say women differ fundamentally from men [Dobson] |
| 23422 | For the environment, affluence and technology matter as much as population size [Dobson] |
| 23425 | Ecologism says growth must be reduced, and efficiency is not enough [Dobson] |
| 23430 | A million years is a proper unit of political time [Dobson] |
| 23423 | We currently value the present fourteen times more highly than the future [Dobson] |