On a Vector Version of a Fundamental Lemma of J. L. Lions

Let Ω be a bounded and connected open subset of ℝ^N with a Lipschitz-continuous boundary, the set Ω being locally on the same side of ∂Ω. A vector version of a fundamental lemma of J. L. Lions, due to C. Amrouche, the first author, L. Gratie and S. Kesavan, asserts that any vector field v = (v_i) ∈ (D'(Ω))^N, such that all the components 1/2(∂_jv_i + ∂_iv_j), 1 ≤ i, j ≤ N, of its symmetrized gradient matrix field are in the space H⁻¹(Ω), is in effect in the space (L²(Ω))^N. The objective of this paper is to show that this vector version of J. L. Lions lemma is equivalent to a certain number of other properties of interest by themselves. These include in particular a vector version of a well-known inequality due to J. Nečas, weak versions of the classical Donati and Saint-Venant compatibility conditions for a matrix field to be the symmetrized gradient matrix field of a vector field, or a natural vector version of a fundamental surjectivity property of the divergence operator.