ctrl u 1/2 up

ctrl d 1/2 down

ctrl e one line down

ctrl y one line up

ctrl b 往上一页 back的意思是回去的意思，所谓回上一页

ctrl f 往下一页 foward是back的反方向，故f下一页

zt move current line to the top of the screen

zb move current line to the bottom of the screen

zz move current line to the middle of the screen

vim screen navigation