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### Ideas of Herbert B. Enderton, by Text

#### [American, fl. 1972, At the University of California, Los Angeles.]

 1977 Elements of Set Theory
 1.03 p.3 13200 Note that {Φ} =/= Φ, because Φ ∈ {Φ} but Φ ∉ Φ
 1:02 p.2 13199 The empty set may look pointless, but many sets can be constructed from it
 1:04 p.4 13201 ∈ says the whole set is in the other; ⊆ says the members of the subset are in the other
 1:15 p.18 13202 Fraenkel added Replacement, to give a theory of ordinal numbers
 2:19 p.19 13203 The singleton is defined using the pairing axiom (as {x,x})
 3:36 p.36 13204 The 'ordered pair' is defined to be {{x}, {x,y}}
 3:48 p.48 13205 We can only define functions if Choice tells us which items are involved
 3:62 p.62 13206 A 'linear or total ordering' must be transitive and satisfy trichotomy
 2001 A Mathematical Introduction to Logic (2nd)
 1.1.3.. p.1 9718 Validity is either semantic (what preserves truth), or proof-theoretic (following procedures)
 1.1.7 p.2 9719 A proof theory is 'sound' if its valid inferences entail semantic validity
 1.1.7 p.2 9720 A proof theory is 'complete' if semantically valid inferences entail proof-theoretic validity
 1.10.1 p.14 9724 Until the 1960s the only semantics was truth-tables
 1.2 p.23 9994 A truth assignment to the components of a wff 'satisfy' it if the wff is then True
 1.3.4 p.4 9721 A logical truth or tautology is a logical consequence of the empty set
 1.6.4 p.10 9723 Sentences with 'if' are only conditionals if they can read as A-implies-B
 1.7 p.62 9996 Expressions are 'decidable' if inclusion in them (or not) can be proved
 1.7.3 p.11 9722 Inference not from content, but from the fact that it was said, is 'conversational implicature'
 2.5 p.142 9995 Proof in finite subsets is sufficient for proof in an infinite set
 2.5 p.142 9997 For a reasonable language, the set of valid wff's can always be enumerated
 Ch.0 p.2 9699 The 'powerset' of a set is all the subsets of a given set
 Ch.0 p.3 9700 Two sets are 'disjoint' iff their intersection is empty
 Ch.0 p.4 9702 A 'domain' of a relation is the set of members of ordered pairs in the relation
 Ch.0 p.4 9701 A 'relation' is a set of ordered pairs
 Ch.0 p.4 9703 'dom R' indicates the 'domain' of objects having a relation
 Ch.0 p.4 9704 'ran R' indicates the 'range' of objects being related to
 Ch.0 p.4 9705 'fld R' indicates the 'field' of all objects in the relation
 Ch.0 p.5 9710 We write F:A→B to indicate that A maps into B (the output of F on A is in B)
 Ch.0 p.5 9707 'F(x)' is the unique value which F assumes for a value of x
 Ch.0 p.5 9706 A 'function' is a relation in which each object is related to just one other object
 Ch.0 p.5 9708 A function 'maps A into B' if the relating things are set A, and the things related to are all in B
 Ch.0 p.5 9709 A function 'maps A onto B' if the relating things are set A, and the things related to are set B
 Ch.0 p.5 9711 A relation is 'reflexive' on a set if every member bears the relation to itself
 Ch.0 p.5 9712 A relation is 'symmetric' on a set if every ordered pair has the relation in both directions
 Ch.0 p.5 9713 A relation is 'transitive' if it can be carried over from two ordered pairs to a third
 Ch.0 p.6 9714 A relation satisfies 'trichotomy' if all pairs are either relations, or contain identical objects
 Ch.0 p.6 9715 An 'equivalence relation' is a reflexive, symmetric and transitive binary relation
 Ch.0 p.6 9716 We 'partition' a set into distinct subsets, according to each relation on its objects
 Ch.0 p.8 9717 A set is 'dominated' by another if a one-to-one function maps the first set into a subset of the second