explaining R. Eliezer. when performing a mitzvah overrides shabbat prohibitions.
and what cases can and cannot be used to derive this principle to apply to others.
(although performing a circumcision is prohibited work on shabbat, the obligation to do this at 8 days overrides shabbat. R.Eliezer holds that other obligations also override shabbat but each need to be derived on a case by case basis as they each have unique aspects to them. for english translation of this talmud page, see here)
