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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def export_stl(mesh):
 """ Convert a Trimesh object into a binary STL file. Parameters --------- mesh: Trimesh object Returns --------- export: bytes, representing mesh in binary STL form """

    header = np.zeros(1, dtype=_stl_dtype_header)
    header['face_count'] = len(mesh.faces)

    packed = np.zeros(len(mesh.faces), dtype=_stl_dtype)
    packed['normals'] = mesh.face_normals
    packed['vertices'] = mesh.triangles

    export = header.tostring()
    export += packed.tostring()

    return export