function uset = find_unbs( cX, jtree )
% function uset = find_unbs( cX, jtree )
% vector of any unmarked neighbouring cluster of cX;
clqs = jtree{1};
nbs  = jtree{3};
xid  = cX.id;
xnb  = nbs{xid};
uset = [];
for i=1:length(xnb)
  yid = xnb(i);
  yclq = clqs{yid};
  if yclq.mark == 0,
	uset = [uset, yid];
  end;
end;