### An immortal fumble by Androcles (19-Sep-2003)

##### Logic is utter gibberish
 ```> > > > > Another simple question: do you know that the expression > > > > > sqrt(1) = 1 xor sqrt(1) = -1 > > > > > implies > > > > > sqrt(1) = 1 or sqrt(1) = -1 > > > > > ? > > > > > > > > > > Dirk Vdm > > > > Wrong again, Ding. Look at a truth table for xor. > > > > A B Xor > > > > 0 0 0 > > > > 0 1 1 > > > > 1 0 1 > > > > 1 1 0 > > > > > > (A xor B) > > > <==> (A and B') or (A' and B) > > > <==> (A or A') and (A or B) and (B' or A') and (B' or B) > > > <==> (A or B) and (B' or A') > > > ==> (A or B) > > > QED > > > > > > Or if you prefer truth tables: > > > A B Or > > > 0 0 0 > > > 0 1 1 > > > 1 0 1 > > > 1 1 1 > > Correct. > > > > > A B Xor > > > 0 0 0 > > > 0 1 1 > > > 1 0 1 > > > 1 1 1 > > Wrong. > > Indeed, that was an obvious typo. Nope. Obvious typos are aloud < (obvious typo, I should have said 'allowed') in written Englihs You could have checked that I used the correct subsitution > in the last part. Nothing to check. Your conclusion is wrong, do your own homework. > So here we go again: > > (A xor B) > <==> (A and B') or (A' and B) > <==> (A or A') and (A or B) and (B' or A') and (B' or B) > <==> (A or B) and (B' or A') > ==> (A or B) > QED > > Or if you prefer truth tables: > A B Or > 0 0 0 > 0 1 1 > 1 0 1 > 1 1 1 > > A B Xor > 0 0 0 > 0 1 1 > 1 0 1 > 1 1 0 > > A B => > 0 0 1 > 0 1 1 > 1 0 0 > 1 1 1 > > (A xor B ) => (A or B) > 0 0 0 1 0 0 0 > 0 1 1 1 0 1 1 > 1 1 0 1 1 1 0 > 1 0 1 1 1 1 1 > QED Utter gibberish. Use a Venn diagram, you should spot your own stupid error. > > Unless you use another kind of logic of course. > > Dirk Vdm Follow-up: > My Venn diagram says that (A xor B) is a subset of (A or B) >   http://users.telenet.be/vdmoortel/dirk/Stuff/AxorB.gif > QED (3) > > Well, I must say that you really did your best: >   http://users.telenet.be/vdmoortel/dirk/Physics/Fumbles/Gibberish.html > Title: "Logic is utter gibberish" What ARE you babbling about? From your own diagram, the intersection that is white is different from the intersection that is blue, and therefore doesn't imply they are the same. Kindly change the title to "Dinky van der Mumble doesn't use or understand logic" ``` Fumble Index Original post & context: 9Iqab.41\$Z_5.9@news-binary.blueyonder.co.uk See also