2,180 reputation
1023
bio website textproof.com/stewart
location Berlin, Germany
age 43
visits member for 3 years, 9 months
seen Apr 4 at 12:40

Freelance copy-editor.


You can read my irregular waffles at advogato.org/person/chalst/.


I have a Math Overflow account.


Apr
4
reviewed Approve suggested edit on Matlab program of a finite sum that returns the result in a matrix
Apr
4
reviewed Approve suggested edit on Powers of permutation matrices.
Apr
3
awarded  Custodian
Apr
3
reviewed Reject suggested edit on From centroid and two vertexes to find the missing vertex of a triangle.
Apr
2
comment What precisely is a vacuous truth?
@MJD: I don't think much of the WP article. It doesn't link its definitions to the sources it lists, and it does not relate to well-known related topics. The claim 'A statement S is "vacuously true" if it resembles the statement $P \Rightarrow Q$, where P is known to be false' is unattributed, imprecise (resembles?, no outermost quantifier?, does "known" mean this is an epistemic claim?) and I would say is false (rather, vacuous truths "resemble" a special case of this form), and the well-known example is generally described as a paradox of material implication.
Apr
2
comment What is the antiderivative of $e^{-x^2}$
What you call the elementary functions, Hardy called the logarithmico-exponential functions: pp. 54-90 of plms.oxfordjournals.org/content/s2-10/1
Dec
13
revised Basic Tautology Question
right != left
Dec
13
answered Basic Tautology Question
Nov
7
answered Deduction Theorem Subtlety and Predicate Proof
Nov
4
awarded  Popular Question
Oct
14
comment Where did mathematicians learn how to do truth tables?
To support what @amWhy says, before his contact with Frege, Wittgenstein's studies were (according to Ian Lemke) in mechanical engineering, physics, philosophy of science and aeronautical engineering. See rsnr.royalsocietypublishing.org/content/61/1/39.full - tyh
Jul
20
awarded  Yearling
Jun
10
answered What is a Herbrand disjunction?
May
15
comment Cardinality of the set of prime numbers
+1 for avoiding Axiom-of-choice -strength principles in your answer.
May
7
awarded  Caucus
May
3
comment Why an inconsistent formal system can prove everything?
@Joshua: All the theorems and valid inference rules involving $\perp$ are still theorems/ valid rules if you substitute that symbol by any other proposition: there is no difference between that symbol and a schematic variable.
Apr
12
comment Direct cut-elimination for natural deduction.
Peter: Thanks; I probably subconsciously "borrowed" from Girard's treatment of the topic in Ch. 10 of Proofs and Types: paultaylor.eu/stable/Proofs+Types.html
Apr
12
comment Direct cut-elimination for natural deduction.
The key innovation in Prawitz's treatment that eluded Gentzen was how he handled formulae in rules with indirect elimination rules, which are needed for disjunction and existential elimination. You need to think of paths of formulae through these rules, and add permutations to the system to ensure that introduction and elimination rules can meet up.
Apr
8
answered Alternative set theories
Nov
14
answered Why is the set of all real numbers uncountable?