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I'm looking for a way to express A being true does not imply B. I know that A implied B can be written as $A \rightarrow B$, but what about A does not imply B? $A \not\rightarrow B$?

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Simply write $A\land\neg B$, though that is probably not what you are after. I think you want something like "$p$ is prime does not imply in general that $p$ is odd", right? –  Hagen von Eitzen Nov 17 '12 at 17:38
    
May be this link help you ftp.dante.de/tex-archive/info/symbols/comprehensive/… –  Babak S. Nov 17 '12 at 17:40
    
@BabakSorouh That tells me how to write the symbol in LaTeX, but not what the symbol means (except possibly by its name). –  gerrit Nov 17 '12 at 17:56
    
@HagenvonEitzen Yes, it's the latter I'm after. –  gerrit Nov 17 '12 at 17:57

2 Answers 2

up vote 3 down vote accepted

If you use a generic $\to$ or $\Rightarrow$ for imply then slash through for the not-imply.

But you can perhaps do better. If you actually mean syntactic entailment (so non-implication is a matter of there being no proof from $A$ to $B$ in the relevant proof system) then $A \nvdash B$ is available and absolutely standard.

If you actually mean semantic entailment (so non-implication is a matter of there being a valuation which makes $A$ true without making $B$ true) then $A \nvDash B$ is available and quite standard.

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Usually, we use double arrows for implications: $A\Rightarrow B$. You can use a crossed out double arrow for does not imply: $A\nRightarrow B$. In LaTeX, these are "\Rightarrow" and "\nRightarrow", respectively.

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