theorem criticalMassJ_characterization {T ρ c d_sq : ℝ}
(hc : 0 < c) (hd : 0 < d_sq) (hρ : ρ < 1) :
2 * criticalMassJ T ρ c d_sq * c ^ 2 * d_sq / (1 - ρ) = T := by
simp only [criticalMassJ]
have h1ρ : (0 : ℝ) ≠ 1 - ρ := by linarith
have hcd : 0 < 2 * c ^ 2 * d_sq := by positivity
field_simpCore definitions for the Lean formalization of Paper 1c: