mathlib3

1ebb2060 - feat(ring_theory/localization): lemmas about `Frac(R)`-spans (#12425)

feat(ring_theory/localization): lemmas about `Frac(R)`-spans (#12425) A couple of lemmas relating spans in the localization of `R` to spans in `R` itself. Co-authored-by: Anne Baanen <Vierkantor@users.noreply.github.com>