theorem gradientNormSq_pos (hJ : 0 < J) : 0 < gradientNormSq J := by simp only [gradientNormSq] exact div_pos one_pos (Nat.cast_pos.mpr hJ)
thesis/CESProofs/Foundations/IsoquantGeometry.lean:38
Differential Geometry of CES Isoquants (Gap #6)