The following looks nice on each of several Mac browsers:
Gμν = 8π Tμν
Gμν = 8π Tμν

But the following is ugly to produce and ugly to view.
T dV
V,t=t0
T dV
V,t=t1
=
t=t1
T dt dS
t=t0

This came from Baez’:

                                               t=t1
       /                  /                    /
       |                  |                    |
       | T dV     -       | T dV       =       | T dt dS
       /                  /                    /
     V,t=t0             V,t=t1                 t=t0
Incidentally I have a very low opinion of math-ml as seen either by the author or the reader. I am not on the sgml bandwagon.