chuáng shàng shī chuáng
比喻多余和重复。
北齐 颜之推《颜氏家训 序致》:“晋魏已来所着诸子,理重事复,递相模效,犹屋下架屋,床上施床耳。”
床上施床作谓语、宾语;指多此一举。
try to fit on a bed where there is a bed already