Euler made the first conjectures about biquadratic reciprocity. There are a number of equivalent ways of stating Burde's rational biquadratic reciprocity law. Gauss published two monographs on biquadratic reciprocity. This was by a 'twisting' argument, implicitly about the L-function of biquadratic fields. The name "biquad" is short for "biquadratic". The relevance of the catalogue is that all these networks are realised by biquadratic functions. Biquadratic fields are all obtained by adjoining two square roots. In the first one (1828) he proved Euler's conjecture about the biquadratic character of 2. SID's audio filter is modeled as an actual two-integrator-loop biquadratic filter. The Kummer extensions in this case also include biquadratic extensions and more general multiquadratic extensions.