Six statements about wavefronts and interference are given below. (i) Light from two sodium lamps gives a steady interference pattern. (ii) Coherent waves of intensity $I_0$ each give $4I_0$ in phase. (iii) A point source at a lens focus gives plane wavefronts. (iv) A small part of a distant spherical wavefront is nearly plane. (v) A wavefront joins points that oscillate with a phase difference of $\pi$. (vi) A reflected plane wave obeys the law of reflection. How many of the statements above are correct?