. . "Examples of cycloalkyl groups which are bonded to a carbon atom in a ring of a compound of this invention via the above-mentioned divalent linking groups and represented by R1 to R4 include, for example, cyclohexyloxy groups, cyclohexylcarbonyl groups, cyclohexyloxycarbonyl groups, cyclohexylamino groups, cyclohexenylcarbonyl groups or cyclohexenyloxy groups, etc." . .