@article{ADM_2008_2_a0,
     author = {Vesselin Drensky and Ralf Holtkamp},
     title = {Planar trees, free nonassociative algebras, invariants, and elliptic integrals},
     journal = {Algebra and discrete mathematics},
     pages = {1--41},
     publisher = {mathdoc},
     number = {2},
     year = {2008},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/ADM_2008_2_a0/}
}