obtain ⟨n, h_card⟩ := VectorSpace.card_fintype Z R
R : Type u_1
inst✝¹ : DecidableEq R
inst✝ : DivisionRing R
h : Fintype R
Z : Subring R := center R
⊢ IsField R
case intro
R : Type u_1
inst✝¹ : DecidableEq R
inst✝ : DivisionRing R
h : Fintype R
Z : Subring R := center R
n : ℕ
h_card : Fintype.card R = Fintype.card ↥Z ^ n
⊢ IsField R