We had a topic about which proof mark people use a while ago, and I was just looking at the common contradiction symbols used on http://en.wikipedia.org/wiki/Contradiction#Symbolic_representation . After doing a logic course I pretty much settled on "up tack" (http://www.fileformat.info/info/unicode/char/22a5/index.htm), probably mainly because it's easy to write.
#2Xshortguy007Posted 6/1/2010 4:12:15 PM
I use the two implication arrows facing each other. ---
http://www.ccc.commnet.edu/grammar/ or www.dianahacker.com/rules
#3linkkhalid89Posted 6/1/2010 6:26:16 PM
I've seen $\perp,\nleftrightarrow$, as well as two which don't show up in the LaTeX script. But I would use $\Rightarrow\Leftarrow$, although I just generally write "this is a contradiction." --- To read the math in my posts, download https://addons.mozilla.org/en-US/firefox/addon/748 and http://www.gold-saucer.org/mathml/greasemonkey/.
#4PaulMalucciMDPosted 6/1/2010 6:57:59 PM
Lightning bolt. --- Rating of LOST S3E15 - 7/10 "Its only like the most awesome hour of television" - Hurley
#5Palex3Posted 6/1/2010 8:58:10 PM
[This message was deleted at the request of the original poster]
#6Palex3Posted 6/1/2010 8:58:39 PM
From: PaulMalucciMD | #004 Lightning bolt.
This. --- His Majesty, Palex the Third, Emperor of all the Canadas, has spoken. Go forth and spread the word.
#7Sir BahamutPosted 6/2/2010 3:49:40 AM
If I'm writing down nicely and neatly I just write "contradiction" or "which gives the required contradiction" or something.
I've gotten quite fond of the lightning bolt for shorthand lately though
--- "You have to be 100% behind someone before you can stab them in the back" ~David Brent.
#8avsfan33Posted 6/2/2010 4:13:21 PM
I just say it. I try to find a good balance between text and symbols. --- Craig Anderson, our Lord and Saviour http://farm3.static.flickr.com/2782/4154343819_8cedebec89.jpg