more on this theme     |     more from this thinker

Single Idea 18249

[filed under theme 6. Mathematics / A. Nature of Mathematics / 3. Nature of Numbers / h. Reals from Cauchy ]

Full Idea

A sequence a1,a2,... of rational numbers is 'Cauchy' if for each rational number ε>0 there is a natural number N such that for all natural numbers m, n, if m>N and n>N then -ε < am - an < ε.

Gist of Idea

Cauchy gave a formal definition of a converging sequence.

Source

Stewart Shapiro (Thinking About Mathematics [2000], 7.2 n4)

Book Ref

Shapiro,Stewart: 'Thinking About Mathematics' [OUP 2000], p.181

A Reaction

The sequence is 'Cauchy' if N exists.

The 15 ideas from 'Thinking About Mathematics'

8725 Rationalism tries to apply mathematical methodology to all of knowledge [Shapiro]
8730 'Impredicative' definitions refer to the thing being described [Shapiro]
8729 Intuitionists deny excluded middle, because it is committed to transcendent truth or objects [Shapiro]
8731 Conceptualist are just realists or idealist or nominalists, depending on their view of concepts [Shapiro]
8744 Logicism seems to be a non-starter if (as is widely held) logic has no ontology of its own [Shapiro]
8749 Term Formalism says mathematics is just about symbols - but real numbers have no names [Shapiro]
8750 Game Formalism is just a matter of rules, like chess - but then why is it useful in science? [Shapiro]
8752 Deductivism says mathematics is logical consequences of uninterpreted axioms [Shapiro]
8753 Critics resent the way intuitionism cripples mathematics, but it allows new important distinctions [Shapiro]
8760 Numbers do not exist independently; the essence of a number is its relations to other numbers [Shapiro]
8761 A 'system' is related objects; a 'pattern' or 'structure' abstracts the pure relations from them [Shapiro]
8763 The number 3 is presumably identical as a natural, an integer, a rational, a real, and complex [Shapiro]
8762 Two definitions of 3 in terms of sets disagree over whether 1 is a member of 3 [Shapiro]
8764 Categories are the best foundation for mathematics [Shapiro]
18249 Cauchy gave a formal definition of a converging sequence. [Shapiro]