“…The relevant density differs according to the specific type of scatteringelectron or scattering length densities for small-angle scattering of X-rays (SAXS) or neutrons (SANS), respectivelybut the mathematics are the same. The apparent simplicity of that statement hides a wealth of difficult questions related notably to the numerical evaluation of correlation functions from scattering data (Glatter, 1977), the determination of nontrivial structural information (Tchoubar & Mé ring, 1969), the development and adjustment of structural models to scattering patterns (Pedersen, 1997;Svergun, 1999), the SAXS analysis of hierarchical structures (Gupta et al, 2006;Gommes et al, 2016), the enumeration of structures compatible with a given correlation function (Gommes et al, 2012a) etc. Any new, albeit mathematically equivalent, perspective on smallangle scattering may shed new light on all these questions as well.…”