 Every prime , non @-@ split alternating knot or link complement has a subdivision rule , with some tiles that do not subdivide , corresponding to the boundary of the link complement . The subdivision rules show what the night sky would look like to someone living in a knot complement ; because the universe wraps around itself ( i.e. is not simply connected ) , an observer would see the visible universe repeat itself in an infinite pattern . The subdivision rule describes that pattern . 
