First of all, b and c are both point sets. Because z is an integer, you can add some numbers to the calculation. When k= 1, B = 7 and C = 3. When k=2, b = 1 1, c = 5；; You will find that the span between two points B is greater than C, that is, the density of point C in the unit interval is greater than that of point B, that is, if B has C, it may not, so,

Set b is contained in set C.

I wonder if I made myself clear (●)? ●) I hope it helps.