Repeating a navigation command in vi

How do I repeat a navigation command in vi?

For example, I execute the command 20j which moves the cursor down 20 lines, and I tried hitting . to repeat that command, but it says "No command to repeat"开发者_JAVA技巧.

P.S. Also, what command goes to the next page in a document?

There isn't a shortcut to repeat the last navigation command - you have to retype it, or set up some sort of shortcut of your own (:map or similar).

Page up (back) is Control-B; page down (forward) is Control-F. Half-pages are Control-U (up) and Control-D (down).