The key [C-M-b] does not work in Emacs.

["numbchild@gmail.com" <numbchild@gmail.com>]

I found Emacs key =[Ctrl-Alt-b]= does not work, but I try its binding
command
=[backward-sexp]= can work. and it does bind to key =[Ctrl-M-b]=, and I use
=[Ctrl-h
k]= (=describe-key=) can capture =[Ctrl-Alt-b]=.

I'm curious might KDE captured this key, but I check out all KDE settings
"Shortcuts", not found. Then I tried command =xev -id <Emacs window ID>= to
capture key under X11. Here is the log:

#+NAME: xev -id [WM_ID]
#+BEGIN_EXAMPLE
FocusOut event, serial 18, synthetic NO, window 0x80008f,
    mode NotifyGrab, detail NotifyVirtual

FocusIn event, serial 18, synthetic NO, window 0x80008f,
    mode NotifyUngrab, detail NotifyVirtual

KeymapNotify event, serial 18, synthetic NO, window 0x0,
    keys:  2   0   0   0   0   0   0   0   5   0   0   0   0   0   0   0
           0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0

PropertyNotify event, serial 18, synthetic NO, window 0x80008f,
    atom 0x16b (_NET_WM_ICON), time 157642247, state PropertyNewValue

PropertyNotify event, serial 18, synthetic NO, window 0x80008f,
    atom 0x23 (WM_HINTS), time 157642248, state PropertyNewValue

ConfigureNotify event, serial 19, synthetic YES, window 0x80008f,
    event 0x80008f, window 0x80008f, (0,57), width 1366, height 711,
    border_width 0, above 0x0, override NO

PropertyNotify event, serial 20, synthetic NO, window 0x80008f,
    atom 0x16b (_NET_WM_ICON), time 157642255, state PropertyNewValue
#+END_EXAMPLE


If anyone knows solution how to solve this problem, please give me some
hints,
thanks very much.


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