Combining Texts
Ideas for
'works', 'Philosophy without Intuitions' and 'Elements of Set Theory'
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8 ideas
4. Formal Logic / F. Set Theory ST / 2. Mechanics of Set Theory / b. Terminology of ST
13201
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∈ says the whole set is in the other; ⊆ says the members of the subset are in the other [Enderton]
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13204
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The 'ordered pair' <x,y> is defined to be {{x}, {x,y}} [Enderton]
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13206
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A 'linear or total ordering' must be transitive and satisfy trichotomy [Enderton]
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4. Formal Logic / F. Set Theory ST / 3. Types of Set / b. Empty (Null) Set
13200
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Note that {Φ} =/= Φ, because Φ ∈ {Φ} but Φ ∉ Φ [Enderton]
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13199
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The empty set may look pointless, but many sets can be constructed from it [Enderton]
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4. Formal Logic / F. Set Theory ST / 3. Types of Set / c. Unit (Singleton) Sets
13203
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The singleton is defined using the pairing axiom (as {x,x}) [Enderton]
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4. Formal Logic / F. Set Theory ST / 4. Axioms for Sets / h. Axiom of Replacement VII
13202
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Fraenkel added Replacement, to give a theory of ordinal numbers [Enderton]
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4. Formal Logic / F. Set Theory ST / 4. Axioms for Sets / j. Axiom of Choice IX
13205
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We can only define functions if Choice tells us which items are involved [Enderton]
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