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It always comes out funky, and I'd like to avoid \nLeftrightarrow. Is there any good way to negate the longer \iff double implication arrow?

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Please ignore my request to close.... It was a misake... – Peter Grill Oct 5 '12 at 3:11
haha no worries man - thanks a ton! – Sean Allred Oct 5 '12 at 3:24
What would $A \not\iff B$ even mean mathematically? It seems to me that saying that exactly one of A or B holds is simpler and clearer. – lhf Oct 5 '12 at 12:09
up vote 6 down vote accepted

You can adapt the solutions form \Rightarrow vs. \implies, and "does not imply" symbol:

enter image description here




$A \notiff B$

$A \centernot\iff B$
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+1 egreg's favourite tool :) – cmhughes Oct 5 '12 at 3:17
I didn't even know something like centernot existed... one wonders why this isn't default behavior! Thanks!! – Sean Allred Oct 5 '12 at 3:23
@vermiculus It isn't the default because those symbols should not be used under any circumstance. They mean nothing, IMHO. – egreg Oct 5 '12 at 6:33
@egreg, in many cases, it is clearer to negate an operator than to negate a predicate (especially when writing for other students). – Sean Allred Oct 10 '12 at 4:28
@vermiculus You're stating a "metanontheorem". Yesterday I was talking about the noncommutativity of matrix multiplication where one cannot say "AB≠BA". Most usages of "doesn't imply" fall under the same case. – egreg Oct 10 '12 at 9:15

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