mathlib

fb5ef2b9 - feat(linear_algebra/nonsingular_inverse): state Cramer's rule explicitly (#4700)

feat(linear_algebra/nonsingular_inverse): state Cramer's rule explicitly (#4700) Mostly so that we can add an entry to the Freek 100. Co-authored-by: Johan Commelin <johan@commelin.net> Co-authored-by: Vierkantor <vierkantor@vierkantor.com>