When students are asked to color a circle on a piece of paper, he explains, they invariably stay within the circle, but he never stipulates that they must stay within the borders!
譬如，他要學生把一張紙上的圓塗滿，大多數學生不假思索便開始在圓內塗色，「但是我並沒有定義『圓內』或『圓外』啊！」