By coincidence i stumbled over this page


<http://www.fields.utoronto.ca/programs/scientific/11-12/exceptional/abstracts.html>


, which was installed for a workshop on algebraic groups in 2012.


In the upper left you will see several Dynkin diagramms of Root Systems.
Just under $F\_4$ there is one named $H\_3$, another one named $H\_4$ and i think there is also $L\_2$.


What are these and where can i found out more about them?



Algebraic Groups of Type H_3 and H_4
It's actually $I\_n$, not $L\_2$ (the print is very small). These diagrams classify finite Coxeter groups ($I\_n$ is the family of dihedral groups and $H\_3$ and $H\_4$ are automorphism groups of certain exceptional polytopes). The three that you mention aren't Weyl groups, so don't come from an algebraic group like the other ones do. More information on the wiki page: <http://en.wikipedia.org/wiki/Coxeter_group#Properties>


