Talk:Exclusive disjunction
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[edit] ((a XOR b) XOR a)
it might be worth explicitly mentioning that given two bytes a and b, ((a XOR b) XOR a) is equal to b. In my opinion, this would aid understanding of the RAID example, and the usefulness of XOR in general. I'm a bit reluctant to do this myself since I haven't edited a page before.
[edit] English semantics
The article says:
- "Exclusive disjunction is the sense of the word or as in the proverb you can have your cake or eat it (but not both)."
I would argue that this is not true, because xor does not allow one to infer either disjunct from the disjunction. In the example, I can infer both
- I can have my cake
- I can eat my cake
which is not supported by the definition of exclusive disjunction. In other words, if the meaning in the proverb were really the exclusive disjunction, it would follow that I had permission to take one of the two actions, but you wouldn't tell me which. Please see e.g. the course notes at [1] for a more detailed explanation.
-- Wmahan. 19:23, 2004 Sep 6 (UTC)
[edit] Precise use of "or" in languages other than English
The articles mentions that some other languages have greater precision in the use of "or". Does anyone have more detailed information on this that can go in the article? ElBenevolente 21:30, 12 Mar 2005 (UTC)
- Latin - aut, utrum, vel. Someone who didn't flunk in Latin fill in the specific meanings of each. ;-) In German, you start the sentence with "entweder" to make clear a later "oder" (or) is meant in the exclusive sense. DevSolar 14:13, 9 May 2006 (UTC)
[edit] check Definition using symbols section
Please check that Definition using symbols section is correct
[edit] More than 2 operands
How is this function defined for more than 2 operands? Alex1 21:25, 10 September 2005 (UTC)
- - The usual version is 'true of an odd number of the propositions'. So e.g. 1 or 3 out of three. Charles Matthews 21:36, 10 September 2005 (UTC)
- - I have found a nice link to explain multiple arguments XOR - Wolfram Mathworld (author-Zbynek Chuchma):
In the meantime I found these port descriptions in the Philips data handbook, part 5: Semiconductors and integrated circuits:
- AND: the output is high if and only if all inputs are high
- NAND: the output is low if and only if all inputs are high
- OR: the output is high if and only if any one or more of the inputs are high
- NOR: the output is low if and only if any one or more of the inputs are high
- EXCLUSIVE-OR: the output is high if and only if any one input is high and all other inputs are low
This explains why it's called exclusive. It's not a parity function. Alex1 10:46, 11 September 2005 (UTC)
- Yes, at present the page is absolutely wrong in its definition for more than two operands. It's a classic wikipediaism. --82.69.188.246 00:01, 23 September 2005 (UTC)
- OK, I could be more charitable about that. It does at least have the decency to contradict itself to raise a proper degree of skepticism in the careful reader:
- "The operation yields the result TRUE when one, and only one, of its operands is TRUE."
- "if there are an odd number of TRUE operands, then the result will be TRUE, otherwise it will be FALSE."
- For clarity, this is the simplest disputable case:
- Popular perception is that the output is 1, but [some] formal definitions have it as 0 because the input is not "any one input high and all others low". The page fails to make this clear and reinforces popular perception by restating, through various reasoning and implication, that it is 1. --ToobMug 23:43, 22 November 2005 (UTC)
[edit] How did this get called "Exclusive Disjunction"?
How did this get called "Exclusive Disjunction"? It's called "Exclusive Or" in real life; I have never heard the phrase "Exclusive Disjunction". Samboy 07:21, 6 October 2005 (UTC)
- OK, I've renamed the article "Exclusive or". Samboy 23:46, 6 October 2005 (UTC)
- FWIW, Googlefight result: 1,750,000 for "Exclusive or" vs. 16,500 for "Exclusive disjunction". Samboy 23:50, 6 October 2005 (UTC)
- It likely comes from the mathematics community since the term "disjunction" is usually preferred over "or". Here's a MathWorld entry on it.--Tokek 03:57, 14 February 2006 (UTC)
I think "Logical inequality" is more appropriate, because OR == Disjunction, but Exclusive OR != Exclusive disjunction. In addition, it is easier to think the meaning of "Logical inequality" than "Exclusive disjunction". QQ 16:16, 28 May 2006 (UTC)
- Hi QQ, I've copied your comment below, and replied to it there. Paul August ☎ 16:39, 28 May 2006 (UTC)
[edit] typo
I'm a little puzzled by some text in the article. Is this a typo?
- ("<u>∨</u>", or ''⊻'')
Should it really be
- ("<u>∨</u>", or ''&;#x22BB;'')
? -- 24.17.192.30 00:07, 2 January 2006 (UTC)
[edit] XNAD and pals
Google searched for both {XNAD "exclusive nand"}[2] and {XNAD "exclusive not and"}[3]. Both returned only this article. Mention of XNAD first appeared: 08:08, 6 November 2005 (UTC).—Tokek
Removed XNAD for now, simply because I don't know and I can't find anything on it. "EOR" and "orr" are also questionable. No note on who/what/when/where/why it would be used, so it's hard to tell if usage has died or not.--Tokek 03:53, 14 February 2006 (UTC)
- I'm 99% sure the assembler in BBC Basic used EOR. and the first couple of results for 6502 instruction set on google also seem to. can't say i've heared either orr or XNAD though. Plugwash 13:25, 14 February 2006 (UTC)
[edit] What's the deal with those exclamation marks !?
JA: Scanning quickly I do not see an explanation of them. Jon Awbrey 17:24, 29 March 2006 (UTC)
- Looks like they mean not from the context. dunno if this is a standard notation though. Plugwash 18:31, 29 March 2006 (UTC)
JA: I've seen that notation for "not" in a hardware context (Spice, etc.), but I think it's best to stick with "~" or "¬" here. Jon Awbrey 18:36, 29 March 2006 (UTC)
[edit] What's with the nbsp?
At the ==In computer science== section:
- It tells whether there are an odd number of 1 bits (A ⊕ B ⊕ C ⊕ D ⊕ E is true iff an odd number of the variables are true).
- " " is the HTML entity for a non-breaking space. Its usage is correct there. --Quuxplusone 00:06, 10 May 2006 (UTC)
[edit] On the use of "+" for XOR
JA: Regarding a comment by Plugwash that was left on the main page:
a plus sign ("+") [!--who actually uses this? i thought a normal plus sign normally meant inclusive or!--]
JA: The use of "+" for exclusive disjunction goes back to Boole and Peirce, as this is the only thing that makes sense in a mathematical framework that places a primary value on ring and field properties. At first, Peirce and Jevons used other symbols for inclusive or, depending on the willingness of various typographers to cut new symbols, and in a pinch Peirce used a plus-and-a-comma (+,) for inclusive or. It seems to have been Schröder who started using "+" for inclusive or, and circuit engineers apparently picked it up from that line of usage. But mathematicians still use "+" in a way that only allows for the XOR reading, and since we have "∨" for inclusive or, there's no point "adding" to the confusion any longer. Jon Awbrey 19:00, 9 May 2006 (UTC)
JA: Nota Bene. "This article is about XOR in the logical sense. For the electronic XOR gate see XOR gate. For other uses, see XOR (disambiguation)."
JA: EE folks have their own article. This article is about the logical and mathematical usages. Jon Awbrey 01:44, 10 May 2006 (UTC)
- Excluding information about symbology used in a particular field is not rational. Not only that, but it warrants specific mention because it's a hazard that people are likely to run into. Exclusive or is a logical operation no matter what field you work in.
- Further, it seems to me that the Alternative symbols section is weighted towards making an argument for particular notations. It currently includes a whole table describing a different operation altogether, which is messy and not relevant to the section heading. --ToobMug 08:41, 18 October 2006 (UTC)
[edit] Re move of page to logical inequality
Earlier today QQ moved this page to logical inequality, with as far as I can tell no prior discussion. I've now moved the page back. I think we should discuss any such much here on the talk page and reach a consensus for any such move. In my opinion "exclusive disjunction" is the traditional and most common name for this concept, especially in philosophy and mathematics. For example a Google search on "exclusive disjunction" gives 23,700 hits, while a Google search on "logical inequality" gives 322 hits. Paul August ☎ 16:25, 28 May 2006 (UTC)
- (I've copied this comment from above)
- I think "Logical inequality" is more appropriate, because OR == Disjunction, but Exclusive OR != Exclusive disjunction. In addition, it is easier to think the meaning of "Logical inequality" than "Exclusive disjunction". QQ 16:16, 28 May 2006 (UTC)
Hi QQ, wikipedia policy (see for example WP:UE) is to use the most commonly used name for a concept as the title of the article about that concept. Paul August ☎ 16:39, 28 May 2006 (UTC)
[edit] Request for external link addition
- I would like to make a formal request to add http://www.celtickane.com/programming/ to the external links section of this page. It is my own website, so I wouldn't like to add it myself, but I would prefer that someone else review the website, and make the decision to add it. It contains an example of XOR encryption in C++. --Sugarskane 03:59, 20 July 2006 (UTC)
- Can you provide a direct link to the example? --Dijxtra 12:16, 20 July 2006 (UTC)
- Of course -- direct link: http://www.celtickane.com/programming/code/XOREncrypt010.cpp --Sugarskane 14:26, 20 July 2006 (UTC)
