“…which again is a complicated infinite-order finite-difference operator on R. However, we already know from previous examples [31,[51][52][53][54][55]70] that when the integrable system is relativistic and has an underlying "modular double" structure, we should in addition consider a "modular dual" Baxter equatioñ and look for two generically linearly independent functions Q (f ) (σ, a, ̵ h y , g y ,ω,ω ′ ) and Q (af ) (σ, a, ̵ h y , g y ,ω,ω ′ ) formally satisfying both (3.72) and (3.73) simultaneously. 18 Similarly to Section 2.5, such formal solutions can conjecturally be obtained by considering the NS limit of the VEVs of codimension two defects corresponding to coupling the fivedimensional theory to two free three-dimensional N = 2 * hypermultiplets, whose SU (2) part of the flavour symmetry is gauged and identified with the five-dimensional gauge group [61][62][63].…”