## WeBWorK Main Forum

### \Longrightarrow (\implies)

by Alex Jordan -
Number of replies: 3
The image for \Longrightarrow (aka \implies if amsmath is loaded) seems like something is wrong with it. I get the jagged arrow you see in the attached image file.

Viewed with jsMath, I get the same kind of thing for \Longrightarrow and an error for \implies.

In LaTeXMathML, I get a nice arrow for \Longrightarrow and an error for \implies.

And MathJax leaves both with a unicode stamp of 27F9.

I can stop using \implies and start using \Longrightarrow, but I'm wondering if the jagged image is a known issue and if there's an easy fix for it.

### Re: \Longrightarrow (\implies)

by Davide Cervone -
TeX creates the \Longrightarrow from an equal sign and \Rightarrow, so what you are seeing is a slight difference in the conversion of those two characters to the pixel grid used in the image. These changes are very sensitive to the size of the fonts used, so it might be possible to fix this by changing the dvipng parameters in your WeBWorK configuration (and removing the cached image from the server).

JsMath uses the same process of creating the long arrow from smaller pieces. Again, the font size on screen can really affect this, so you might try zooming in or out to see if there is an improvement.

For LaTeXMathML, you are converting to MathML, and (assuming you are using Firefox), this will use a single glyph for the arrow, so it should look good, provided you have an appropriate font that includes it. Apparently LaTeXMathML doesn't have a definition for \implies. That could probably be added.

MathJax uses single-character glyphs for these arrows, (the unicode character is at U+27F9, as you note). But if you are seeing the missing character symbol, then something may be wrong with your installation. If you use the MathJax contextual menu and select About MathJax, what font mode does it tell you (directly below the MathJax version at the top of the dialog box that appears)? You should see something like "using local STIX fonts". What OS and browser are you using (and what versions)?

Davide

### Re: \Longrightarrow (\implies)

by Alex Jordan -
Thanks Davide,

I went to look to answer your question, and \Longrightarrow is working now in MathJax. Earlier I was on a fairly old Mac laptop with an old OS and an old web browser, so that may explain why I was seeing unicode stamps.

It's strange to me that this is how TeX creates \Longrightarrow. It seems inelegant by TeX standards.