n number of identical equilateral prisms are kept in contact as shown in figure. If deviation through a single prism is $\mathrm{\delta }$ Then (n, m are integers)

if n=2m, deviation through system of n prism is $\mathrm{\delta }$

if n=2m+1, deviation through system of n prism is $\mathrm{\delta }$

if n=2m+1, deviation through system of n prism is zero

if n=2m, deviation through n prisms is zero