(McCleary's User Guide to Spectral Sequences pg 458)
I refer to the statement "We denote the $E^1$-term by $B_n^1\cong H_n(X;\mathbb{F}_p)$".
Is $B_n^1\cong H_n(X;\mathbb{F}_p)$ just a definition, or is it the result of some theorem? I am a bit confused since $B_n$ is sometimes used to denote boundary group, i.e. the image of the differential. Or does B just stand for Bockstein here (i.e. it is just a definition to be accepted)?
Thanks for any help.