數列an <= bn <= cn,<an>,<cn>均收斂且<bn>發散

數列an <= bn <= cn對所有自然數n都成立,<an>,<cn>均收斂且<bn>發散

請問  有沒有例子說明這段話

謝謝

舉例:
<an>=<-2>={-2,-2,................,-2,...........}
<bn>=<(-1)^n>={-1,1,-1,1,...........,(-1)^n,..............}
<cn>=<2>={2,2,................,2,...........}