Thanks Willy2. It is an English version, I believe.
Thanks jpm. Eventually I found the entry in the context menu inserted by windows repair - it was entitled "open", and I had not found it before because it was not present in the context menu of a .reg file, although I did find it in the context menu of a .rtf file. I also created my another entry following the instructions you referred me to, and that did cause Open with Notepad, as I had named the key, to appear in the context menu. The only difference between the key created by windows repair and the key I created manually so far as I could see was that I had named the subkey "Command", whereas that in the key created by windows repair was named "command". I noticed that I was unable to change the name of either key only by changing the case from upper to lower, or vice versa, but on trying to do so got a message that the registry editor could not rename it because a key of the name chosen already existed. This suggested that the naming is not case sensitive, and so I can only wonder why the entry made by windows repair would not appear in the context menu of a .reg file.
I will send some images.