Hot answers tagged emacs
The direct answer is probably that vi is part of the POSIX standard (as @jasonwryan also mentioned in a comment), as well as the Single UNIX Specification. As such, anything that calls itself POSIX-compliant probably includes something vi-like, and anything that wants to call itself UNIX has to, or you don't get certified. Not just vi, but the related line ...
If this happens often, consider running your emacs session in the Gnome Terminal withintmux. That way you can connect from the console with tmux attach and save whatever needs saving. If you don't use tmux, reptyr can allow you to reconnect the emacs session to your console for further editing. Setting emacs` autosave might help as well in case you have ...
If you are specifically interested in avoiding interference of markdown-mode with math enclosed in $...$ or $$...$$, you can do M-x markdown-enable-math while markdown major mode is on, see http://jblevins.org/projects/markdown-mode/
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