mathlib

9fb53f98 - chore(analysis/calculus/fderiv_symmetric): Squeeze some simps in a very slow proof (#8609)

chore(analysis/calculus/fderiv_symmetric): Squeeze some simps in a very slow proof (#8609) This doesn't seem to help much, but is low-hanging speedup fruit that the next person stuck on a timeout here will inevitably want solved first. Co-authored-by: sgouezel <sebastien.gouezel@univ-rennes1.fr>