convert coprime_one_right _
this : Fact (Nat.Prime 5)
⊢ Coprime 5 (Fintype.card (ClassGroup (𝓞 (CyclotomicField ⟨5, ⋯⟩ ℚ))))
case h.e'_2
this : Fact (Nat.Prime 5)
⊢ Fintype.card (ClassGroup (𝓞 (CyclotomicField ⟨5, ⋯⟩ ℚ))) = 1