Set Extension

# Set Extension For a given set of two-dimensional points S, let's denote its extension E(S) as the result of the following algorithm: Create another set of two-dimensional points R, which is initially equal to S. Then, while there exist four numbers x1, y1, x2 and y2 such that (x1,y1)∈R, (x1,y2)∈R, (x2,y1)∈R and (x2,y2)∉R, add (x2,y2) to R. When it is impossible to find such four integers, let