cyclic organic compound 計唔計係SAME HOMOLOGOUS SERIES

我想問homologous series ge definition 係咩??
因為我睇cclee organic chem 書ge 時候佢話 ' a homologous seires is a series of compounds with adjacent members differing in their formula by a -CH2- unit' , ' Note that two compounds with the same functional group need not be the members of the same homologous seies. For example, ethanol and cyclohexanol are not homologous'
但係我睇neway 書佢就話有the same functional group 都算係。到底實情係點? 呢d cyclic compound 計唔計埋??