We have a binary relation on $Z^2$: $(x_1, y_1)R(x_2, y_2) \iff x_1 \leq x_2, y_1 \leq y_2$. Find maximal elements in the following set: $F = \{(x, y)|x^2 + y^2 \leq 4\}$.
We can't say that it is $(2,2)$ because it's not in $F$. Any ideas?
Thank you for your help.