  I show that Sudakov resummation takes a particularly transparent form if one
deals with the second logarithmic derivative of the short distance coefficient
functions for deep inelastic scattering and the Drell-Yan process. A uniquely
defined Sudakov exponent emerges, and I conjecture that the leftover constant
terms not included in the exponent are given by the second logarithmic
derivative of the massless quark form factor. The meaning of a previously
obtained large $N_f$ evidence for an infrared finite perturbative Sudakov
coupling is reconsidered. This coupling is reinterpreted as a Minkowskian
coupling, making the introduction of a low-energy non-perturbative modification
of the corresponding Euclidean coupling a priori necessary. Some hints for a
Banks-Zaks type of fixed point in the Euclidean coupling at finite $N_f$ are
nevertheless pointed out, and strong evidence is provided in favor of its
universality. A criterion to select in a unique way the proper Euclidean
Sudakov coupling relevant to the issue of power corrections is suggested.
