2

In the thread Symbol for "defined to be logically equivalent" (:⇔), we discussed how to tex ":⇔" correctly. As we learnt, the solution is to define the following new command:

\newcommand*{\logeq}{\ratio\Leftrightarrow}

Now, this only works with

\Leftrightarrow

I am interested in how to tex the "colon \iff" correctly, that is, with a

\Longleftrightarrow

instead of a

\Leftrightarrow
  • What does it look like if you just substitute the commands? Does it not look "correct"? If so, why? – Werner Aug 24 '16 at 18:52
  • \Longleftrightarrow (or, which is the same, \iff) generates space in front and behind it. – CantBelieve Aug 24 '16 at 18:56
  • The spacing isn't that much different when you use \ratio\Longleftrightarrow (picture) compared to using \iff. Why do you need to use \iff? – Werner Aug 24 '16 at 19:01
  • @Werner: Thanks, you are right. I thought \Longleftrightarrow would be the same as \iff. But the issue with the spacing only arises with \iff. Your comment is worth an answer. :-) – CantBelieve Aug 24 '16 at 19:04
  • \ratio\Longleftrightarrow should be good; not \iff (that's not really supported in LaTeX). – egreg Aug 24 '16 at 19:27
1

\iff is similar to \Longleftrightarrow but forces an amount of space on either side - a \; or \thickmuskip (see What commands are there for horizontal spacing?). That,

\def\pshow#1{{\let\protect\show#1}}
\pshow\iff

yields

> \iff =\long macro:
->\;\Longleftrightarrow \;.
\iff ->\protect \iff  

in the .log. In contrast,

\pshow\Longleftrightarrow

yields

> \Longleftrightarrow =\long macro:
->\Leftarrow \joinrel \Rightarrow .

in the .log - a \join or the relations \Leftarrow and \Rightarrow, without adding spaces around the outside.

\documentclass{article}
\usepackage{colonequals}
\newcommand*{\logeq}{\ratio\Leftrightarrow}
\newcommand*{\longeq}{\ratio\Longleftrightarrow}
\begin{document}
\[ A \logeq B \longeq C \]
\end{document}
| improve this answer | |
  • I guess for those using \iff elsewhere it makes sense to use \newcommand*{\longeq}{\;\ratio\Longleftrightarrow\;} so that the spacing comes out the same. – Daniel Sep 22 '19 at 8:56

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.