Solution
= Solution
For the <L12 structure>, the <crystal basis structure factor> is
$$
F_{hkl}=f_{\rm Sc}+f_{\rm Al}\left[e^{i\pi(h+k)}+e^{i\pi(h+l)}+e^{i\pi(k+l)}\right].
$$
Equal parity of $h,k,l$ makes all three phase factors $+1$, hence
$$
\boxed{F_{hkl}=f_{\rm Sc}+3f_{\rm Al}}.
$$
The <electron> scattering factors are evaluated at the reflection's scattering vector.