because it's not a list. Look at the documentation of the fonction generating it.

• Consider x,y coordinates of a box.
• Consider the histogram is rotated to the left so that the bars are displayed vertical.

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• So h is the height of the bar for the current i
• And j looks left and right (from i) to see how far the width w can increase before it hits the each or misses a bar

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• Now given height h and width w I can check the area of this box to see if it is biggest