This simple model simulates the classic Polya urn problem in which stones, either black or white, are randomly selected (with replacement) from a pot. The user begins with two stones, one of each color. Each time a stone of a given color is selected, the stone is replaced and another stone of the same color is added to the pot. Therefore, the odds of adding a stone of a given color is always equal to the proportion of that color currently in the pot.
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