问题
I somehow managed to define the 'M' (capital em) key as a prefix key in sqlplus-mode which is preventing me from typing an M.
How can I unset this prefix key in this mode?
回答1:
Short term fix:
M-x local-set-key M self-insert-command
Long term fix, find the spot in your .emacs file which defines it a ssuch. @tripleee's comment does sound like a likely candidate for what went wrong.
来源：https://stackoverflow.com/questions/10820058/emacs-undefine-prefix-key