English
If χ is primitive but e is not primitive, then gaussSum χ e = 0.
Русский
Если χ примитивен, но e не примитивен, то gaussSum χ e = 0.
LaTeX
$$$\\text{gaussSum\\_eq\\_zero\\_of\\_isPrimitive\\_of\\_not\\_isPrimitive}: χ.IsPrimitive \\rightarrow ¬ e.IsPrimitive \\rightarrow gaussSum χ e = 0.$$$
Lean4
/-- If `χ` is primitive, but `e` is not, then `gaussSum χ e = 0`. -/
theorem gaussSum_eq_zero_of_isPrimitive_of_not_isPrimitive [IsDomain R] {χ : DirichletCharacter R N}
(hχ : IsPrimitive χ) (he : ¬IsPrimitive e) : gaussSum χ e = 0 :=
by
contrapose! hχ
rcases e.exists_divisor_of_not_isPrimitive he with ⟨d, hd₁, hd₂, hed⟩
have : χ.conductor ≤ d := Nat.sInf_le <| factorsThrough_of_gaussSum_ne_zero e hd₁ hed hχ
exact (this.trans_lt hd₂).ne