“…In fact, if N = 2, taking Pα = ∇α, α ∈ C ∞ (R 2 , R), Qγ = curl γ = ∂γ 2 /∂x−∂γ 1 /∂y, γ ∈ C ∞ (R 2 , R 2 ) then one has an elliptic complex and Pα, Q * β is equal to the determinant of the matrix whose rows are given by ∇α, ∇β. In this case, the lower semicontinuity has been studied in a series of papers (see for instance [AD,ADMM,CD,DM2,DS,FH,G,M1,M2,Ma1,Ma2]).…”