Compactness and contradiction.

Terence Tao

American Mathematical Society

Publication Year: 2013

ISBN-10: 0-8218-9492-7

ISBN-13: 978-0-8218-9492-7

Last updated: Apr 28, 2016

This continues my series of books derived from my blog. The preceding books in this series were “Structure and Randomness“, “Poincaré’s legacies“, “An epsilon of room“, “An introduction to measure theory“, “Topics in random matrix theory“, and “Higher order Fourier analysis“.

A draft version of the MS can be found here.

Pre-errata (corrected in the published version):

- Page 78: In the first paragraph, “at least the” should be “at least one of the”. In the second paragraph, “generated by ” and “generated by ” should be “generated by ” and “generated by ” respectively. In the third paragraph, after the first sentence, add “We may take to be a normal subgroup of “. In the last paragraph, replace “cannot grow polynomially” by “cannot grow exponentially (as otherwise the number of subsums of for and would grow exponentially in , contradicting the polynomial growth hypothesis)”
- Page 79, footnote 12: replace the first sentence by “Proof: the algebraic integers for natural number have bounded degree and all Galois conjugates bounded, so the minimal polynomials have bounded integer coefficients and must thus repeat themselves after finitely many .”

Errata:

- Page 92: In the third display, should be .
- Page 94: “quarternionic” should be “quaternionic” (two occurrences).
- Page ???: In the paragraph before (3.17), (3.13) should be (3.12).
- Page 110: “considing” should be “considering”.
- Page 131: in Section 3.10.2, at the end of the treatment of the non-transverse case, “the exponent of here is positive” should be “the exponent of here is negative”.
- Page 220?: In Section 5.4.1, all occurrences of should be .

Thanks to Benjamin Sprung, Felix Voigtlaender, Bill Zajc, and an anonymous contributor for corrections.

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1 July, 2011 at 10:49 am

Compactness and contradiction « What’s new[…] of the last of my books based on my 2010 blog posts (and also my Google buzzes), entitled “Compactness and contradiction“. The PDF of this draft is available here. This is a somewhat assorted (and lightly […]

14 July, 2011 at 10:01 am

TomSmall error (of a non-mathematical nature) on page 153

“each of the constants, operations, and relations as

anelements, functions, and relations”[Thanks, this will be corrected in the next version of the ms – T.]18 August, 2016 at 9:35 am

BriefcaseJoeThis comment concerns the first subsection “1.1 Material implication”:

Interpreting “If A, then B” as saying “B is at least as true as A” sheds bright light on how one can prove the equivalence of two or more statements, that is, that they have the same truth value: Given “If A, then B” and “If B, then A”, we can infer that A is both at least and at most as true as B, allowing us to conclude that A and B are equivalent. In general, if we have proven a chain of implication of the form

then we can interpret this as saying that is at least as true as , that is at least as true as etc. and that * is at least as true as *. Thus, the statements , , …, are equivalent.

Indeed, until learning this way of looking at implications I didn’t fully understand proof by contrapositive (which is also evident when interpreting “If A, then B” as “B is at least as true as A” and “If not B, then not A” as “A is at least as false as B”) and the method of proving the equivalence of several statements discussed above. Does this mean that I am stupid? Or are there other ways of understanding these proof methods?

I am also wondering why this way of looking at implications isn’t mentioned in other text books or on the internet. Can you guys find an explanation of that?