I'm following the Latex howto of org-mode babel. Here's the snippet from the howto I've got in a separate .org file (see bottom of howto page):

#+LATEX_HEADER: \usepackage{tikz}

First execute the second code block, to define the convenience macro

and to set the required new variables in ob-latex.el.  Then export to

HTML and to pdf to see the tree exported as an SVG image and as

embedded tikz respectively.

* Tikz test

Here's a tree, exported to both html and pdf.

#+header: :file (by-backend (html "tree.svg") (t 'nil))

#+header: :imagemagick

#+header: :results (by-backend (pdf "latex") (t "raw"))

#+header: :tangle yes

#+begin_src latex

  \usetikzlibrary{trees}

  \begin{tikzpicture}

    \node [circle, draw, fill=red!20] at (0,0) {1}

    child { node [circle, draw, fill=blue!30] {2}

      child { node [circle, draw, fill=green!30] {3} }

      child { node [circle, draw, fill=yellow!30] {4} }};

  \end{tikzpicture}

#+end_src

* COMMENT setup

#+header: :tangle yes

#+begin_src emacs-lisp :results silent

  (setq org-babel-latex-htlatex "htlatex")

  (defmacro by-backend (&rest body)

    `(case (if (boundp 'backend) (org-export-backend-name backend) nil) ,@body))

#+end_src

This doesn't really produce a .svg of the tree as advertised, but exporting to Latex does produce it just fine.

My real confusion starts when I try to tangle the babel code blocks. The C-c C-v t command produces two separate files just fine, a .tex and .el, but then if I try to Run Latex on the .tex file just by itself it gives an error. Here's what the org-mode tangle produces:

\usetikzlibrary{trees}

\begin{tikzpicture}

  \node [circle, draw, fill=red!20] at (0,0) {1}

  child { node [circle, draw, fill=blue!30] {2}

    child { node [circle, draw, fill=green!30] {3} }

    child { node [circle, draw, fill=yellow!30] {4} }};

\end{tikzpicture}

And here's the error log after I try to run it by itself in Emacs:

. . .entering extended mode

 restricted \write18 enabled.

 file:line:error style messages enabled.

 %&-line parsing enabled.

**\input prac2.tex

(./prac2.tex

./prac2.tex:2: Undefined control sequence.

l.2 \usetikzlibrary

                   {trees}

The control sequence at the end of the top line

of your error message was never \def'ed. If you have

misspelled it (e.g., `\hobx'), type `I' and the correct

spelling (e.g., `I\hbox'). Otherwise just continue,

and I'll forget about whatever was undefined.

Another version (from C-c `) produces this error message:

ERROR: Undefined control sequence.

--- TeX said ---

l.2 \usetikzlibrary

                   {trees}

--- HELP ---

TeX encountered an unknown command name. You probably misspelled the

name. If this message occurs when a LaTeX command is being processed,

the command is probably in the wrong place---for example, the error

can be produced by an \item command that's not inside a list-making

environment. The error can also be caused by a missing \documentclass

command.

What am I missing here? I'd like to be able to keep my org stuff separate from the Latex source, which org-mode seems to do nicely. But then it has to run properly too. . . .

LB