Sentence:  Corollary 1. — "The <WSD>convex envelope</WSD> of a subset "A" of "E" is identical with the set of linear combinations \sum_i\lambda_i x_i, where (x_i) is any finite family of points in A, the numbers \lambda_i > 0 for all i and \sum_i \lambda_i = 1." 
Meaning of the word marked with <WSD> tags:  Convex hull.