The bellows conjecture for small flexible polyhedra in non-Euclidean spaces

The bellows conjecture claims that the volume of any flexible polyhedron of dimension 3 or higher is constant during the flexion. The bellows conjecture was proved for flexible polyhedra in the Euclidean spaces of dimensions 3 and higher, and for bounded flexible polyhedra in the odd-dimensional Lobachevsky spaces. Counterexamples to the bellows conjecture are known in all open hemispheres of dimensions 3 and higher. The aim of this paper is to prove that, nonetheless, the bellows conjecture is true for all flexible polyhedra in either spheres or Lobachevsky spaces of dimensions greater than or equal to 3 with sufficiently small edge lengths.