“…The geometrical interpretation of (1) as an Euler-Poincaré equation naturally generalizes to diffeomorphisms in two or more dimensions, and the analogues of the weak solutions (2) can be applied to the problem of template matching in computational anatomy [15]; but in general such higher-dimensional extensions do not to preserve integrability. Further research on the one-dimensional case has been concerned with the derivation [12,27] and classification [26] of integrable scalar equations analogous to (1), as well as the search for suitable two-component or multi-component analogues [6,10,16,19,32,31,33,34]. From the analytical point of view, there is also considerable interest in finding dispersive equations with higher order nonlinearity, which (despite not being integrable) display similar features in the form of peakons, wave breaking and one or more higher conservation laws [1,14].…”