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LyX is a wysiwyg LaTeX editor that I find useful to write exercises fast instead of TextMate that I use for long-term projects. So the below shows an exercise that I would like to print as PDF: however I am getting the following errors Undefined control sequence that are very vague. I cannot see any \begin{document} or other LaTeX commands in LyX in the view which makes debugging harder than in text-based editors. So
How can I compile a document in LyX?
Document > Settings > LaTeX Preamble
and add your preamble such as \usepackage{amsmath,amsfonts,amssymb,amsthm}
so
and CMD+R to get the document compiled like in TextMate -- it works without writing any \begin{document}.
Document > Settings > Math Options
More graphical method as pointed out by the comment is to tongle the settings in Math Options like the below and in this case you don't need to add the mathematical packages to LaTeX Preamble.
\mathbbis what's unidentified means thatamsfonts(or if you need more symbols,amssymb, which loadsamsfonts) isn't loaded. so try adding that to your job. (but i don't know how, not being a lyx user.) – barbara beeton Mar 4 '16 at 17:51