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I found in the manual that implies is the right kind of arrow tip, so I tried


  \draw[<->,double equal sign distance,implies] (2,1) -- (3,2);

But somehow, implies breaks <->, such that only one end of the line gets an arrow tip.

So how do I get the equivalence as arrow in Tikz?

I searched for another suitable arrow tip (like equivalent) or another suitable parameter instead of <-> to say that both line ends should get the arrow tip, but did not find anything.

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how to obtain an equivalence with a colorful side please ? – Vrouvrou Mar 4 '15 at 6:12
up vote 12 down vote accepted

implies is the name of a TikZ arrowhead (defined in the arrows TikZ library). It has to be combined with a hyphen (as in my code); it cannot be used as a PGF key on its own (as in your MWE). The following code produces the desired output:

enter image description here

\draw[implies-implies,double equal sign distance] (2,1) -- (3,2);
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Ohhhhh, so implies is just like < and > (and the direction is automatically correct). Thanks. – DaveBall aka user750378 Aug 24 '13 at 17:20
Before a confusion arises: >=implies and then <-> works too. The comment with the hypen just means that implies is a arrow head just like latex or to or … – Qrrbrbirlbel Aug 24 '13 at 18:47
@Qrrbrbirlbel please how to obtain an equivalence with a colorful side? – Vrouvrou Mar 4 '15 at 6:08

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