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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 projection(self, exprs):
 """ Like mutate, but do not include existing table columns """

        w = self._get_window()
        windowed_exprs = []
        exprs = self.table._resolve(exprs)
        for expr in exprs:
            expr = L.windowize_function(expr, w=w)
            windowed_exprs.append(expr)
        return self.table.projection(windowed_exprs)