We obtain a reduction of the vectorial Ribaucour transformation that preserves the class of submanifolds of constant sectional curvature of space forms, which we call the L -transformation. It allows to construct a family of such submanifolds starting with a given one and a vector-valued solution of a system of linear partial differential equations. We prove a decomposition theorem for the L -transformation, which is a far-reaching generalization of the classical permutability formula for the Ribaucour transformation of surfaces of constant curvature in Euclidean three space. As a consequence, we derive a Bianchi-cube theorem, which allows to produce, from k initial scalar L -transforms of a given submanifold of constant curvature, a whole k -dimensional cube all of whose remaining 2 k - ( k + 1 ) vertices are submanifolds with the same constant sectional curvature given by explicit algebraic formulae. We also obtain further reductions, as well as corresponding decomposition and Bianchi-cube theorems, for the classes of n -dimensional flat Lagrangian submanifolds of C n and n -dimensional Lagrangian submanifolds with constant curvature c of the complex projective space C P n ( 4 c ) or the complex hyperbolic space C H n ( 4 c ) of complex dimension n and constant holomorphic curvature 4c.