theorem positive_externality {J ρ : ℝ} (hJ : 0 < J) (hρ : ρ < 1) : 0 < marginalK J ρ := pigouvian_subsidy_pos hJ hρ
thesis/CESProofs/EntryExit/Welfare.lean:64
Paper 1c, Section 4: Welfare and Coordination Failure