How to indent several lines(one region) left?

[Wu Kejia]

Hi,

Everyone, I can indent several lines right now with Cx TAB, but how to 
indent these lines left? I refer the manual, Cx TAB maps the function 
indent-rigidly, with argument. If the argument is negative, indent left. 
Where should I input the argument? I try to type Mx indent-rigidly RET, but 
without any chance for me to input an argument. I run emacs on windows. 
Thanks for any response. Thanks.

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