mathlib

99138604 - feat(ring_theory/tensor_product): add assoc for tensor product as an algebra homomorphism (#13309)

feat(ring_theory/tensor_product): add assoc for tensor product as an algebra homomorphism (#13309) By speeding up a commented out def, this goes from from ~100s to ~7s on my machine . Co-authored-by: Scott Morrison <scott@tqft.net>