On a theorem of Ritt and related Diophantine problems. Michael Fried (1973) Journal für die reine und angewandte Mathematik
On the extension of valuations on a field K to K ( X ) . - I Nicolae Popescu, Constantin Vraciu (1992) Rendiconti del Seminario Matematico della Università di Padova
On valued function fields II. Regular functions and elements with the uniqueness property. B. Green, M. Matignon, F. Pop (1990) Journal für die reine und angewandte Mathematik