mathlib3

68aada0d - feat(algebra/algebra/spectrum): prove the spectral mapping theorem for polynomials (#10783)

feat(algebra/algebra/spectrum): prove the spectral mapping theorem for polynomials (#10783) Prove the spectral mapping theorem for polynomials. That is, if `p` is a polynomial and `a : A` where `A` is an algebra over a field `𝕜`, then `p (σ a) ⊆ σ (p a)`. Moreover, if `𝕜` is algebraically closed, then this inclusion is an equality. Co-authored-by: Vierkantor <vierkantor@vierkantor.com>