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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 pathway(F, A, B):
 r"""Compute the dominant reaction-pathway. Parameters F : (M, M) scipy.sparse matrix The flux network (matrix of netflux values) A : array_like The set of starting states B : array_like The set of end states Returns ------- w : list The dominant reaction-pathway """

    if F.nnz == 0:
        raise PathwayError('no more pathways left: Flux matrix does not contain any positive entries')
    b1, b2, F = find_bottleneck(F, A, B)
    if np.any(A == b1):
        wL = [b1, ]
    elif np.any(B == b1):
        raise PathwayError(("Roles of vertices b1 and b2 are switched."
                            "This should never happen for a correct flux network"
                            "obtained from a reversible transition meatrix."))
    else:
        wL = pathway(F, A, [b1, ])
    if np.any(B == b2):
        wR = [b2, ]
    elif np.any(A == b2):
        raise PathwayError(("Roles of vertices b1 and b2 are switched."
                            "This should never happen for a correct flux network"
                            "obtained from a reversible transition meatrix."))
    else:
        wR = pathway(F, [b2, ], B)
    return wL + wR