I may offer you an angle here: xpy uses x and y because x and y could be vectors, but can also be matrices mm can not be used for vectors, only for matrices.

I may offer you an angle here: xpy uses x and y because x and y could be vectors, but can also be matrices mm can not be used for vectors, only for matrices. Of course, the main reason is that these are names used for the last 40+ years in the standard for this type of software, BLAS.