  A systematic framework for jet definition is developed from first principles
of physical measurement, quantum field theory, and QCD. A jet definition is
found which: is theoretically optimal in regard of both minimization of
detector errors and inversion of hadronization; is similar to a cone algorithm
with dynamically negotiated jet shapes and positions found via shape
observables that generalize the thrust to any number of axes; involves no ad
hoc conventions; allows a fast computer implementation [hep-ph/9912415]. The
framework offers an array of options for systematic construction of
quasi-optimal observables for specific applications.
