nextval
x = nextval (x, 1);
x = nextval (x, -1);
x = nextval (x, -1);
x = nextval (x, 1);
x = nextval (x, -1);
x = nextval (x, -1);
x = nextval (x, 1);
x = nextval (x, -1);
x = nextval (x, -1);