Re: keep|flush-lines, how-many to be used backward.

[Richard Stallman]

        What I fail to agree with, is that a prefix argument can be a
        three-state boolean=A0: present, negative or positive.  

    It is straight forward to provide three options or two depending on
    whether the code distinguishes between a list and an integer.

I don't really like the idea of that much complexity.
If you want anything unusual you can set up a region.
It doesn't happen often enough to be worth saving a few characters in.