In STL files Euler’s rule for solids can be written as a.No. of faces – No. of edges + No. of vertices = 3 x No. of bodies b.No. of faces – No. of edges + No. of vertices = No. of bodies c.No. of faces – No. of edges + No. of vertices = 2 x No. of bodies d.No. of faces – No. of edges + No. of vertices = 4 x No. of bodies