FiL RB trees

A Red-Black-Tree Formalization for LMU's Formalization in Lean (FiL) WS 2024/25.

Graphviz

def exTree1 : Raw Int := .node (.node .nil 0 .red .nil) 2 .black (.node .nil 3 .red .nil)
#eval IO.FS.writeFile "examples/tree-preinsert.gv" exTree1.toGraphviz

Then execute the following command on a machine with graphviz installed:

dot -Tsvg tree.gv -o tree.svg

or the following for png:

dot -T png tree.gv -O

and you can look at the rendered file.