mathlib3

8b1f3237 - feat(ring_theory/polynomial): Almost Vieta's formula on products of (X + r) (#5696)

feat(ring_theory/polynomial): Almost Vieta's formula on products of (X + r) (#5696) The main result is `prod_X_add_C_eq_sum_esymm`, which proves that a product of linear terms is equal to a linear combination of symmetric polynomials. Evaluating the variables of the symmetric polynomials gives Vieta's Formula. Co-authored-by: Bryan Gin-ge Chen <bryangingechen@gmail.com>