I know "expose one more line" for Ctrl-E, but why use Ctrl-Y to expose one more line at the top? Is there an easy mnemonic for this that I'm missing?
Bill Joy and Mark Horton wrote in their original vi manual:
If you want to see more of the file below where you are, you can hit
^Eto expose one more line at the bottom of the screen, leaving the cursor where it is. The command
^Y(which is hopelessly non-mnemonic, but next to
^Uon the keyboard) exposes one more line at the top of the screen.
So, "next to u" was the motivation, and can serve as a mnemonic, I guess.
The Y also sort of represents an arrow pointing up (↑) if you squint a little bit (it has the head of the arrow inverted).