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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 state_reachable(subsystem):
 """Return whether a state can be reached according to the network's TPM."""

    # If there is a row `r` in the TPM such that all entries of `r - state` are
    # between -1 and 1, then the given state has a nonzero probability of being
    # reached from some state.
    # First we take the submatrix of the conditioned TPM that corresponds to
    # the nodes that are actually in the subsystem...
    tpm = subsystem.tpm[..., subsystem.node_indices]
    # Then we do the subtraction and test.
    test = tpm - np.array(subsystem.proper_state)
    if not np.any(np.logical_and(-1 < test, test < 1).all(-1)):
        raise exceptions.StateUnreachableError(subsystem.state)