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

## closed as off-topic by Najib Idrissi, TMM, user61527, Asaf Karagila♦, Davide GiraudoMar 20 '14 at 21:16

This question appears to be off-topic. The users who voted to close gave this specific reason:

• "This question does not appear to be about Mathematics Stack Exchange or the software that powers the Stack Exchange network within the scope defined in the help center." – Najib Idrissi, TMM, Community, Asaf Karagila, Davide Giraudo
If this question can be reworded to fit the rules in the help center, please edit the question.

\Rightarrow\!\Leftarrow gives $\Rightarrow\!\Leftarrow$. There's a good argument that words are better, though.
• 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". – Hurkyl Mar 12 '14 at 19:43
• 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 $\Longrightarrow$. – GEdgar Mar 14 '14 at 14:55