arising from its generalisation. The earliest example concerns the possibility of Cooper pairs having angular momentum quantum number $ l>0 $, thus breaking the rotational symmetry of the continuum [@Balian-64; @Anderson-Brinkman-74]. Such speculations were based on the assumtion of a different *shape* of the potential describing the effective attraction between fermions. Another generalisation concerned *stronger* values of the fermion-fermion attraction. It was realised that there is a crossover, as this strength is increased, from a BCS superfluid to a Bose-Einstein condensate of non-overlapping pairs [@Eagles-69], with a dramatic effect on the critical temperature [@Pincus-et-al-73]. It turned out that the ground state can be described by a straightforward generalisation of BCS theory [@Leggett-80], while the superconducting instability requires taking into account “preformed pair” (PP) fluctuations in the normal state [@Nozieres-SchmittRink-85].

Experimentally, Cooper pairing with $ l>0 $ was first observed in the superfluid state of $ ^{3} $He. Moreover since the discovery of superconductivity in cuprate preovskites [@Bednorz-Muller-86], whose pairs have $ d_{x^{2}-y^{2}} $ symmetry [@Annett-Goldenfeld-Leggett-96], several families of “anomalous superconductors” have been found. Many of these materials present exotic pairing in the form of a superconducting state that breaks the rotational symmetry of the crystal, and they often deviate from 