amsmath requires amsgen

[nbeisert]

amsmath uses definitions of the support package amsgen such as \@xp and many others, but it only includes amsgen indirectly through amstext, amsopn and amsbsy. In practice, this causes no problems, but it makes the code less transparent. In fact, amsmath would continue to compile and work fine without these packages, but not without amsgen. For what it's worth, I'd suggest to explicitly require amsgen before the other three packages:

latex2e/required/amsmath/amsmath.dtx

Line 349 in 0e10f72

\RequirePackage{amstext}[1995/01/25]