u    -- Undo command.

           default range                 syntax
                .                         u[d]

        1.  "u" is used to undo modifications to  a  line  immediately
        after  changes  are  made.  E.g.  if you substituted "pat" for
        "hat" in a line, to reverse that operation immediately, simply
        type "u" (RETURN).

        2.  "ud" is used to restore a group of lines  that  have  been
        delete  E.g.   if  "n,md"  deletes lines n thru m, then if you
        position the curser to line n-1 and  issue  "ud"  the  deleted
        lines  will  appear.   (Or you can set the od toggle to od< so
        that the line pointer is automatically set to n-1.

        To return to the command directory, type "hcomdir."
        See also:  "hd" and "hod".