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### 9.2 Why does Emacs say ‘`Key sequence XXX uses invalid prefix characters`’?

Usually, one of two things has happened. In one case, the control character in the key sequence has been misspecified (e.g., ‘`C-f`’ used instead of ‘`\C-f`’ within a Lisp expression). In the other case, a prefix key in the keystroke sequence you were trying to bind was already bound as a complete key. Historically, the ‘`ESC [`’ prefix was usually the problem, in which case you should evaluate either of these forms before attempting to bind the key sequence:

    (global-unset-key [?\e ?[])  ;;  or
    (global-unset-key "\e[")