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| | [No title] (Site not responding. Last check: 2007-10-31) |
 | | We say that a rectangle is _in F_ if the four points (x_1,y_1), (x_1,y_2), (x_2,y_1), (x_2,y_2) are in F. Lemma: The set of all rectangles in [0,1]^4 which are in F has positive measure with respect to \mu_1(x_1) \mu_1(x_2) \mu_2(y_1) \mu_2(y_2). |
 | | For each rectangle (x_1,x_2,y_1,y_2) in Y, the measure (f_1(x_2) \delta(x-x_1) - f_1(x_1) \delta(x-x_2)) (f_2(y_2) \delta(y-y_1) - f_2(y_2) \delta(y-y_2)) is supported on F and has horizontal and vertical projections both equal to zero when multiplied by f_1(x) f_2(y). |
 | | It is easy to show that this measure is absolutely continuous and thus of the form h(x,y) dx dy for some measurable h. |
| www.math.niu.edu /~rusin/known-math/99/measures (467 words) |
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