# How to type =|| = in MathJax?

I want to type the following symbol (for logical equivalence):

Some editors have the command \DashvDash available, but SE's MathJax doesn't.
Alternatively, the symbol can be defined via \reflectbox{\vDash}\!\vDash, but this requires the package graphicx which isn't included either.

How can I render the above symbol in SE's MathJax?

• Doesn't $\equiv$ suffice? \equiv – amWhy Jun 22 '20 at 15:54
• No, some sources reserve $\equiv$ for syntactic identity (and I also prefer the analogy to $\vDash$ over a completely different looking symbol). – lemontree Jun 22 '20 at 16:16

The commands \DashvDash and \dashVdash in LaTeX are part of the stix package. As far as I can tell, they are not available in MathJax. However, you could use Unicode. (These symbols can be found in the Unicode block Miscellaneous Mathematical Symbols-A.) Or you could simply copy-paste them when needed.

• $⟛$ and $⟚$ produces $$⟛$$ and $$⟚$$
• $\unicode{x27DA}$ and $\unicode{x27DB}$ produced $$\unicode{x27DA}$$ and $$\unicode{x27DB}$$

You might also use \mathrel to get the required spacing. (In the stix package in LaTeX, this is a relation symbol.) Compare $$x \mathrel{⟛} y$$ and $$x ⟛ y$$. (Obtained by $x \mathrel{⟛} y$ and $x ⟛ y$.)

If you have a post where you use this symbol often, you might want to create a shortcut. For example, after including $\newcommand{\DvD}{\mathrel{\unicode{x27DB}}}$ you can then simply use in the post \DvD whenever you need this command. (I have avoided using the standard name from the stix package on purpose - it seems better not to redefine standard macros. We do not know whether these commands might be implemented in MathJax at some point in the future.)

Example: $$\newcommand{\DvD}{\mathrel{\unicode{x27DB}}}\DvD$$.

I would have included some examples similar to the actual usage of this symbol - but I am not familiar with it.

How does $$=\hspace{-5pt}|\hspace{-.5pt}|\hspace{-5pt}=$$ look?
