## contour lines

I must plot contour lines of ( $arcsin(x)+arcsin(y)-arcsinx\sqrt{1-y^2}+y\sqrt{1-x^2}=c$) , for c=Pi and c=0. I have tried to use Maple and Graph to do this, bet it doesn't work out very well. I know that for c=Pi there is only one point (1;1), but neither Maple or Graph shows that. Also it seems that for c=0 there is infinite number of points (x;y).
Can i find these contour lines in analitical way?