  Symmetrization of bosonic wave functions produces bunching and low
temperature phenomena like Bose-Einstein condensation, superfludity,
superconductivity, as well as laser. Since probability is conserved, one might
expect such bunchings at one place would lead to a depletion or a destructive
interference at another place. This indeed takes place in high-energy
scatterings, leading to cancellations between Feynman diagrams with permuted
(real or virtual) boson lines. It is such cancellation that allow the Froissart
bound to be obeyed, and the meson-baryon amplitudes in large-N_c QCD to be
consistent. These lectures review the derivation and some of the applications
of ``nonabelian cut diagrams'', which are resummation of Feynman diagrams, but
with these interference effects explicitly incorporated. Unlike the traditional
method where cancellations occur between Feynman diagrams, making it necessary
to compute each diagram to subleading orders, destructive interference has been
taken care of from the start in nonabelian cut diagrams. No further
cancellation takes place, so each nonabelian cut diagram may be computed only
in the leading order.
