as according to special relativity the relative speed is u'=(u-v)/1-(uv)/c^2=0/0$u'=\frac{(u-v)}{1-(uv)/c^2}=\frac{0}{0}$ because v=c$v=c$ the speed of second photon with respect to any inertial observer and u=c spee$u=c$ speed of first photon with respect to same observer so u'$u'$ the speed of first with respect to second photon should also be c$c$ according to second postulate of special relativity but how
