  Another possible explanation for the failure of λ-independence is that the apparatus settings influence the pair's state at the source, and accordingly the distribution of the possible pairs' states λ is dependent upon the settings. Since the settings can be made after the emission of the particle pair from the source, this kind of violation of λ-independence would require backward causation. (For advocates of this way out of non-locality, see Costa de Beauregard 1977, 1979, 1985, Sutherland 1983, 1998, 2006 and Price 1984, 1994, 1996, chapters 3, 8 and 9.) On some readings of John Cramer's (1980, 1986) transactional interpretation of quantum mechanics (see Maudlin 1994, pp. 197-199), such violation of λ-independence is postulated. According to this interpretation, the source sends ‘offer’ waves forward to the measurement apparatuses, and the apparatuses send ‘confirmation’ waves (from the space-time regions of the measurement events) backward to the source, thus affecting the states of emitted pairs according to the settings of the apparatuses.  The question of whether such a theory can reproduce the predictions of quantum mechanics is a controversial matter (see Maudlin 1994, pp. 197-199, Berkovitz 2002, section 5, and Kastner 2006). It is noteworthy, however, that while the violation of λ-independence is sufficient for circumventing Bell's theorem, the failure of this condition per se does not substantiate locality. The challenge of providing a local model of the EPR/B experiment also applies to models that violate λ-independence. (For more about these issues, see sections 9 and 10.3.)