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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:

def cleanUpFlow(self, river, world):
        '''Validate that for each point in river is equal to or lower than the
        last'''
        celevation = 1.0
        for r in river:
            rx, ry = r
            relevation = world.layers['elevation'].data[ry, rx]
            if relevation <= celevation:
                celevation = relevation
            elif relevation > celevation:
                world.layers['elevation'].data[ry, rx] = celevation
        return river