32 ideas
17749 | Post proved the consistency of propositional logic in 1921 [Walicki] |
17765 | Propositional language can only relate statements as the same or as different [Walicki] |
17764 | Boolean connectives are interpreted as functions on the set {1,0} [Walicki] |
17752 | The empty set is useful for defining sets by properties, when the members are not yet known [Walicki] |
17753 | The empty set avoids having to take special precautions in case members vanish [Walicki] |
17759 | Ordinals play the central role in set theory, providing the model of well-ordering [Walicki] |
17741 | To determine the patterns in logic, one must identify its 'building blocks' [Walicki] |
17747 | A 'model' of a theory specifies interpreting a language in a domain to make all theorems true [Walicki] |
17748 | The L-S Theorem says no theory (even of reals) says more than a natural number theory [Walicki] |
17761 | A compact axiomatisation makes it possible to understand a field as a whole [Walicki] |
17763 | Axiomatic systems are purely syntactic, and do not presuppose any interpretation [Walicki] |
17757 | Members of ordinals are ordinals, and also subsets of ordinals [Walicki] |
17755 | Ordinals are the empty set, union with the singleton, and any arbitrary union of ordinals [Walicki] |
17756 | The union of finite ordinals is the first 'limit ordinal'; 2ω is the second... [Walicki] |
17760 | Two infinite ordinals can represent a single infinite cardinal [Walicki] |
17758 | Ordinals are transitive sets of transitive sets; or transitive sets totally ordered by inclusion [Walicki] |
17762 | In non-Euclidean geometry, all Euclidean theorems are valid that avoid the fifth postulate [Walicki] |
17754 | Inductive proof depends on the choice of the ordering [Walicki] |
17486 | Supervenience is simply modally robust property co-variance [Hendry] |
17742 | Scotus based modality on semantic consistency, instead of on what the future could allow [Walicki] |
17481 | Nuclear charge (plus laws) explains electron structure and spectrum, but not vice versa [Hendry] |
1748 | Archelaus was the first person to say that the universe is boundless [Archelaus, by Diog. Laertius] |
17478 | Maybe two kinds are the same if there is no change of entropy on isothermal mixing [Hendry] |
17479 | The nature of an element must survive chemical change, so it is the nucleus, not the electrons [Hendry] |
17485 | Maybe water is the smallest part of it that still counts as water (which is H2O molecules) [Hendry] |
17484 | Maybe the nature of water is macroscopic, and not in the microstructure [Hendry] |
17482 | Compounds can differ with the same collection of atoms, so structure matters too [Hendry] |
17483 | Water continuously changes, with new groupings of molecules [Hendry] |
17476 | Elements survive chemical change, and are tracked to explain direction and properties [Hendry] |
17477 | Defining elements by atomic number allowed atoms of an element to have different masses [Hendry] |
17480 | Generally it is nuclear charge (not nuclear mass) which determines behaviour [Hendry] |
5989 | Archelaus said life began in a primeval slime [Archelaus, by Schofield] |