The tangent bundle T X of a world manifold X and the associated principal frame bundle F X of linear tangent frames in T X possess a general linear group structure group G L + ( 4 , R ) . A world manifold X is said to be parallelizable if the tangent bundle T X and, accordingly, the frame bundle F X are trivial, i.e., there exists a global section (a frame field) of F X . It is essential that the tangent and associated bundles over a world manifold admit a bundle atlas of finite number of trivialization charts.