Thank you Konstantin, your explanation seems more or less watertight and very similar to the explanation offered by Geraint Jones a few days ago. It may be that a non-native speaker with an analytical bent can 'see' more clearly than a native speaker. A residual problem remains with 'wyneb' however as, in many parts of Wales, the word is considered to be 'gwyneb' (where I come from, it is said 'gwynab') and it is a surprise to many to find that the elemental form of the word is 'wyneb'. When speaking, I would always use 'y', as in the following sentence:'Mae o'n nofio ar y gwyneb'(He's swimming on the surface). If I were forced to drop the 'g', I would find great difficulty in using 'yr'. This raises the issue of local dialect vs faulty grammar i.e. true dialect is a 'correct' form, but can faulty grammar, if it is used long enough, be thought of as dialect? John Williams, Saudi Arabia