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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 fibs(n, m):
 """ Yields Fibonacci numbers starting from ``n`` and ending at ``m``. """

    a = b = 1
    for x in range(3, m + 1):
        a, b = b, a + b
        if x >= n:
            yield b