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Analytic signals are introduced as certain eigenfunctions of the Hilbert transform operator; that is, is termed "analytic" if and only if for all , where is the Hilbert transform of . Similarly, "dual-analytic" signals are defined as solutions of the homogeneous equation . Using this characterization of analytic signals (shown to be equivalent to the usual definition due to Ville ), simple proofs are obtained for all known product theorems of the form , which are useful in the representation and analysis of modulated waveforms. In addition, parallel theorems for the class of dual-analytic and frequency-translated dual-analytic signals are proven.