TikZ test
This method is reused.
TODO
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Automate the generation of TikZ diagrams.
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Add counter to TikZ diagrams.
Demo
Similarly, we can construct the second cohomology of Lie algebras for classifying central extensions. An exact sequence of Lie algebras
is call a central extension if \(\lie{a}\) is abelian and \([\lie{a},\lie{b}]=0\).