% Five people sitting at a round table hold
% positive or negative integer values with a
% total of zero.  At least one of them holds
% a non-zero value initially.
% A person holding a negative number -n (n>0)
% can negate it (i.e., increase it by 2n) by
% subtracting n from each neighbor.
% Is it possible that this process evetually
% terminates (i.e., ends up with five zeros)? 

X=[1,2,3,-2,-4|X].

X=[A0,B0,C0|Y] :-
  B0<0, A=A0+B0, C=C0+B0, B=-B0 |
  X=[A,B,C|Y].
  