The Lagrange reconstructing polynomial [Shu C.W.: SIAM Rev. 51 (2009) 82-126] of a function f (x) on a given set of equidistant (∆x = const) points x i + ℓ∆x; ℓ ∈ {−M − , · · · , +M + } is defined as the polynomial whose sliding (with x) averages on [x − 1 2 ∆x, x + 1 2 ∆x] are equal to the Lagrange interpolating polynomial of f (x) on the same stencil [Gerolymos G.A.: J. Approx. Theory 163 (2011) 267-305]. We first study the fundamental functions of Lagrange reconstruction, show that these polynomials have only real and distinct roots, which are never located at the cellinterfaces (half-points) x i + n 1 2 ∆x (n ∈ Z), and obtain several identities. Using these identities, we show that there exists a unique representation of the Lagrange reconstructing polynomial on {i − M − , · · · , i + M + } as a combination of the Lagrange reconstructing polynomials on Neville substencils [Carlini E., Ferretti R., Russo G.: SIAM J. Sci. Comp. 27 (2005) 1071-1091], with weights which are rational functions of ξ (x = x i + ξ∆x) [Liu Y.Y., Shu C.W., Zhang M.P.: Acta Math. Appl. Sinica 25 (2009) 503-538], and give an analytical recursive expression of the weight-functions.We show that all of the poles of the rational weight-functions are real, and that there can be no poles at half-points. We then use the analytical expression of the weight-functions, combined with the factorization of the fundamental functions of Lagrange reconstruction, to obtain a formal proof of convexity (positivity of the weight-functions) in the neighborhood of ξ = 1 2 , iff all of the substencils contain either point i or point i + 1 (or both).