  The rules of soft-collinear effective theory can be used naively to write
hard scattering cross-sections as convolutions of separate hard, jet, and soft
functions. One condition required to guarantee the validity of such a
factorization is the infrared safety of these functions in perturbation theory.
Using e+e- angularity distributions as an example, we propose and illustrate an
intuitive method to test this infrared safety at one loop. We look for regions
of integration in the sum of Feynman diagrams contributing to the jet and soft
functions where the integrals become infrared divergent. Our analysis is
independent of an explicit infrared regulator, clarifies how to distinguish
infrared and ultraviolet singularities in pure dimensional regularization, and
demonstrates the necessity of taking zero-bins into account to obtain
infrared-safe jet functions.
