This differs from the Nsnal expression, which includes the core interaction (st,gsl Uslg~rtv) as well T. his usual result is obtained if, in the first term of Eq. (10) (which we know to be identically zero), we replace X, t+& by its Born approximation p . In this approximation, this term is no longer zero, since rt, and P, are eigenfunctions of different Hamiltonians. The result is just the extra term found by perturbation techniques. It is clear that this term should rot be present, and that only the inadequacies of the perturbation approach have led to its appearance. Some of the virtues of an approach in which the exact expression is obtained before approximations are made can be seen from this example.We may also observe that the so-called "post-prior" discrepancy has evaporated. This discrepancy arises when the ordinary (but incorrect) perturbation result is used, since then either U or U& may enter the expression for M&~". While formally they give identical results, that is (rt y&l U I@ st&)= (st y&l && ly Its); when approximate bound-state wave functions are introduced into these matrix elements, the equality no longer holds.We now see that this term should not be present at all and that no problem exists.It. is proved that a two-body reaction amplitude involving scalar particles and satisfying Mandelstam's representation is bounded by expressions of the form Csin's at the forward and backward angles, and Cs4 ln&s at any other fixed angle in the physical region, C being a constant, s being the total squared c.m. energy. This corresponds to cross sections increasing at most like ln s. These restrictions limit the freedom of choice of the subtraction terms to six arbitrary single spectral functions and one subtraction constant.

The amount of contextuality is quantified in terms of the probability of the necessary violations of noncontextual assignments to counterfactual elements of physical reality.

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