and 12 respectively of module 10b these common edges lie in the vertical limit plane 25 the sides of modules 10a and 10b lie in the same plane 25 with the edge of triangular component 15 of module 10a sharing an edge with triangle 11 of module 10b triangle 22 of 10a sharing an edge with triangle 16 of 10b triangle 11 of 10a sharing an edge with triangle 15 of 10b and triangle 16 of 10a sharing an edge with triangle 22 of 10b the hypotenuses of the triangles 16 18 20 and 22 forming the boundary between modules 10 and 10a lie in limit plane 26 the hypotenuses of the same triangles forming the boundary between modules 10b and 10c lie in limit plane 27 equally spaced on the opposite side of the vertical plane the hypotenuses of triangles 12 and 14 defining the short base of module 10 and the short sides of triangles 11 and 16 and 15 and 22 defining the sides of module 10 all lie in a base plane 28 spaced from plane 26 by the same distance that plane 26 is spaced from vertical plane 25 similarly the same edges of module 10c lie in base plane 29 which is similarly spaced in most instances planes 28 and 29 will be coplanar being the plane at which the base of the structure is attached to a foundation or to the ground the parts are constrained to lie in their respective planes to form a rigid mathematically determinate structure by anchoring the components 11 12 14 15 16 and 22 of modules 10 and 10c whose edges lie in the base planes.