@article{1103907599, author = {R\"ussmann, H. and Zehnder, E.}, title = {On a normal form of symmetric maps of $[0,\,1]$}, journal = {Comm. Math. Phys.}, volume = {71}, number = {1}, year = {1980}, pages = { 49-53}, language = {en}, url = {http://dml.mathdoc.fr/item/1103907599} }
Rüssmann, H.; Zehnder, E. On a normal form of symmetric maps of $[0,\,1]$. Comm. Math. Phys., Tome 71 (1980) no. 1, pp. 49-53. http://gdmltest.u-ga.fr/item/1103907599/