sentences:  On top of this, add a rectangular layer of width "x"1 and height "A"/"x"1, so it also has area "A".The top of this layer is at height "y"2 = "y"1 + "A"/"x"1, and intersects the density function at a point ("x"2, "y"2), where "y"2 = "f"("x"2).This layer includes every point in the density function between "y"1 and "y"2, but (unlike the base layer) also includes points such as ("x"1, "y"2) which are not in the desired distribution.