  The analyticity properties of the S matrix in the physical region are
determined by the correspondence principle, which asserts that the predictions
of classical physics are generated by taking the classical limit of the
predictions of quantum theory. The analyticity properties deducible in this way
from classical properties include the locations of the singularity surfaces,
the rules for analytic continuation around these surfaces, and the analytic
character (e.g., pole, logarithmic, etc.) of these singulatities. These
important properties of the S matrix are thus derived without using stringent
locality assumptions. The quantum properties are derived by an analytic reverse
engineering of the classical properties.
