Timeline for Reductio ad absurdum or the contrapositive?
Current License: CC BY-SA 2.5
19 events
| when toggle format | what | by | license | comment | |
|---|---|---|---|---|---|
| Mar 18, 2021 at 10:46 | answer | added | Michael Greinecker | timeline score: 4 | |
| Oct 21, 2010 at 21:58 | answer | added | Artem Kaznatcheev | timeline score: 6 | |
| Aug 3, 2010 at 2:17 | comment | added | Kaveh | considering your first minor question, I think the reason is this: people prefer to have fewer negations in their theorems, IMHO, they prefer to think of theorems as constructively as possible, even when the proof is not. So in place of saying "if there is no foo, then there is no bar", people prefer "if there is a bar, then there is a foo". | |
| Aug 3, 2010 at 2:11 | comment | added | Kaveh | Proof by contradiction (, i.e. derive $\Delta \vdash \varphi$ from $\Delta, \lnot \varphi \vdash \bot$) is not valid in intuitionistic logic. Proof by contrapositive (, i.e. derive $\Delta \vdash \psi \rightarrow \varphi$ from $\Delta \vdash \lnot \varphi \rightarrow \lnot \psi$) is neither. It is not hard to see that intuitionistic logic plus each gives the classical logic. | |
| Aug 3, 2010 at 2:00 | comment | added | Kaveh | seems to be related to this question: gowers.wordpress.com/2010/03/28/… | |
| Feb 10, 2010 at 5:43 | history | made wiki | Post Made Community Wiki by Harry Gindi | ||
| Jan 20, 2010 at 17:04 | answer | added | Terry Tao | timeline score: 48 | |
| Jan 20, 2010 at 10:17 | comment | added | Harry Gindi | WRt that post, I only unaccepted it because you said it was incorrect. In general, I don't change answers once I accept them unless it turns out that the information is wrong. | |
| Jan 20, 2010 at 10:03 | vote | accept | Harry Gindi | ||
| Jan 20, 2010 at 9:50 | comment | added | Charles Stewart | Wrt. your comment on Pete's post, you can change which answer you consider accepted: click on the green tick to unselect, and then you can choose again. | |
| Jan 20, 2010 at 9:37 | answer | added | Joel David Hamkins | timeline score: 144 | |
| Jan 20, 2010 at 3:02 | answer | added | Pete L. Clark | timeline score: 35 | |
| Jan 20, 2010 at 1:22 | vote | accept | Harry Gindi | ||
| Jan 20, 2010 at 9:58 | |||||
| Jan 20, 2010 at 0:21 | answer | added | user1437 | timeline score: 3 | |
| Jan 20, 2010 at 0:16 | history | edited | Harry Gindi | CC BY-SA 2.5 |
added 158 characters in body
|
| Jan 19, 2010 at 23:46 | answer | added | François G. Dorais | timeline score: 30 | |
| Jan 19, 2010 at 23:44 | history | edited | Harry Gindi | CC BY-SA 2.5 |
added 176 characters in body
|
| Jan 19, 2010 at 23:37 | answer | added | compguy | timeline score: 7 | |
| Jan 19, 2010 at 22:26 | history | asked | Harry Gindi | CC BY-SA 2.5 |