Are there symbols for contradiction for a proof by contradiction? I tried $\lightning, \Lightning$.

To clarify, there's no code for lightning? I believed it'd be shorter than \Rightarrow\!\Leftarrow


1 Answer 1


\Rightarrow\!\Leftarrow gives $\Rightarrow\!\Leftarrow$. There's a good argument that words are better, though.

  • $\begingroup$ I would write "For the purpose of deriving a contradiction suppose that blah, blah." Then I would end with "This is the desired contradiction." Perhaps the latter statement might include equation numbers. $\endgroup$
    – Jay
    Mar 6, 2014 at 15:17
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    $\begingroup$ thanks. why are words better? $\endgroup$
    – user53259
    Mar 12, 2014 at 16:27
  • $\begingroup$ @Tucker: Because everybody understands "Contradiction!" whereas notation depends on convention much more than words. $\endgroup$
    – Asaf Karagila Mod
    Mar 12, 2014 at 16:47
  • $\begingroup$ And I don't think any particular convention is widespread; the symbol I drew above (or maybe it was $\rightarrow\!\leftarrow$) was introduced to me by one of my professors, but I don't think I've ever seen it in a book. Similarly, I don't think I've ever seen the \lightning symbol you mention before. As Asaf said, everyone knows "contradiction". $\endgroup$
    – user14972
    Mar 12, 2014 at 19:43
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    $\begingroup$ Words are better, yes. Except when you have to write fast, and do not expect strangers to read the result. The same comment applies to a lot of other symbolism. Write "and" instead of writing $\wedge$. Write "if...then" instead of writing $\Longrightarrow$. $\endgroup$
    – GEdgar
    Mar 14, 2014 at 14:55