Identify the true statements in the following :
(i) If a curve is symmetrical about the origin, then it is symmetrical about both the axes.
(ii) If a curve is symmetrical about both the axes, then it is symmetrical about the origin.
(iii) A curve f(x,y)=0 is symmetrical about the line y=x if f(x,y)=f(y,x).
(iv) For the curve f(x,y)=0 if f(x,y)=f(−y,−x) then it is symmetrical about the origin.