The main purpose of these notes is to present, under precisely stated assumptions, the basic real-variable theory of regularly varying functions, in self-contained manner. Thus they may be used by any reader wishing to acquire a user's knowledge of this valuable analytical tool, irrespective of his field of mathematical specialization. With these aims in mind, the author has endeavoured to keep proofs simple where possible and exercises have been provided to show the scope of the theory as well as to yield practice in the use of the material presented.
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