Situation: I am sitting on a sofa chair with a window behind me.
Alternative situations: I started reading a book in this sofa chair, there is good light because there is a window behind me and also, I got a cup of coffee on top of the coffee table in front of me. Having opened the window behind me, I am sitting on a chair and noticing a spot on a coffee table in front of me.
Question: What is on the wall to my left that you use an eraser and marker with?