o that m and n are not 0 at the same time, and when m or n is an integer of not less than 2, the R.sup.7 or the R.sup.8 may be bonded to each other to form a ring; Q is a bridging group of the two 5-membered rings, andis a divalent hydrocarbon group having 1 to 20 carbon atoms, a divalent halogenated hydrocarbon group having 1 to 20 carbon atoms, a silylene or an oligosilylene group which may be s