isabelle/valid/mathd_numbertheory_466.thy (11 lines of code) (raw):

(* Authors: Wenda Li *) theory mathd_numbertheory_466 imports Complex_Main "HOL-Computational_Algebra.Computational_Algebra" "HOL-Number_Theory.Number_Theory" begin theorem mathd_numbertheory_466: "(\<Sum> k< 11. k) mod 9 = (1::nat)" by eval end