A Proof of the Axion?
  We show that the de Sitter quantum breaking bound when applied to QCD exposes
the necessity of the axion solution to the strong CP problem. The Peccei-Quinn
mechanism emerges as a consistency requirement independent of the naturalness
questions. The $\theta$-angle must be unphysical rather than simply small. All
other approaches including a fine-tuning of $\theta$ lead to the existence of
de Sitter vacua and are excluded by consistency.
