I found in the manual that implies is the right kind of arrow tip, so I tried
\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{arrows}
\begin{document}
\begin{tikzpicture}[>=latex]
\draw[<->,double equal sign distance,implies] (2,1) -- (3,2);
\end{tikzpicture}
\end{document}
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.
