13 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] |
8404 | Explain single events by general rules, or vice versa, or probability explains both, or they are unconnected [Field,H] |
8401 | Physical laws are largely time-symmetric, so they make a poor basis for directional causation [Field,H] |
8400 | Identifying cause and effect is not just conventional; we explain later events by earlier ones [Field,H] |
8402 | The only reason for adding the notion of 'cause' to fundamental physics is directionality [Field,H] |
13605 | Gravity isn't a force, because it produces effects without diminishing [Mayer] |