Is it possible for N to be negative?
Is it possible that N < 0? and |N| > P?
Yes, counter-clockwise encirclements give N < 0 since N is the number of clock-wise encirclements if you have two counter-clockwise encirclements of the -1 point then N = -2.
If N is not equal to -P then the closed loop system will be unstable.
--Mary Dunlop 15:58, 6 November 2006 (PST)