REF="../concepts/source.html">Source</A>, <A HREF="../concepts/sink.html">Sink</A>, <A HREF="../concepts/input_filter.html">InputFilter</A> and <A HREF="../concepts/output_filter.html">OutputFilter</A>. The full sets of requirements for the Filter and Device concepts are summarized in the definitions of the concepts <A HREF="../concepts/device.html">Device</A> and <A HREF="../concepts/filter.html">Filter</A> which form the roots of the concept hierarchies.
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    To ease the task of defining new Filte