Use Retin-A exactly as your doctor has prescribed it for you. Follow all directions on your prescription label. Do not use this medicine in larger or smaller amounts or for longer than recommended. Do not take by mouth. Retin-A is for use only on the skin.
Definition of wall for English Language Learners : a structure of brick, stone, etc., that surrounds an area or separates one area from another : the structure that forms the side of a room or building
Wall comes from Latin vallum meaning ...an earthen wall or rampart set with palisades, a row or line of stakes, a wall, a rampart, fortification... while the Latin word murus means a defensive stone wall English uses the same word to mean an external wall and the internal sides of a room, but this is not universal.