# One way implication, one way no implication

I would like to make 2 implication arrows on top of one another, facing opposite directions, such that the bottom one is actually a not implies. I would also like to be able to label these arrows with text.

• Welcome to TeX SX! Should these arrows be extensible in function of the text? – Bernard Apr 23 at 22:32
• Maybe you want to have a look here and see if you can modify it to your needs. – user121799 Apr 23 at 22:46

Does that answer me as described in your question? There are three types of examples, with the hope that I have answered correctly.

\documentclass[a4paper,12pt]{article}
\usepackage{amsmath,amssymb}
\usepackage{scalerel}

\begin{document}
$a\mkern10mu\Rightarrow \mkern-30mu\nLeftarrow\mkern10mu b$
$a \nLeftrightarrow b$
$a \overset{\,\scaleobj{1.5}{\Rightarrow}}{\nLeftarrow} b$
\end{document}


A version which is correctly centred on the math axis and scales accordingly to the math style.

\documentclass{article}

\usepackage{amssymb}

\def\impliesnotimpliedby{\mathrel{\mathpalette\impliesnotimpliedbyaux\relax}}
\def\impliesnotimpliedbyaux#1#2{%
\vcenter{%
\offinterlineskip
\hbox{$#1\;\Rightarrow$}\vskip.3ex\hbox{$#1\nLeftarrow$}
}%
}

\begin{document}

$A \impliesnotimpliedby B_{A \impliesnotimpliedby B_{A \impliesnotimpliedby B}}$

\end{document}


• Then the last of the three I've written is like yours and I'm glad. Your code is better than mine surely. – Sebastiano Aug 19 at 15:40