[1] Borel A. Le plan projectif des octaves et les sphères comme espaces homogènes. C R Acad Sci Paris, 1950, 230: 1378-1380 [2] Griffiths P A. Complex differential and integral geometry and curvature integrals associated to singularities of complex analytic varieties. Duke Math J, 1978, 45(3): 427-512 [3] Howard R. The kinematic formula in Riemannian homogeneous spaces. Mem Amer Math Soc, 1993, 106(509): 1-69 [4] Montgomery D, Samelson H. Transformation groups of spheres. Ann of Math, 1943, 44(3): 454-470