Mass-radius relation exponent ζ_L (Sect. 3.2) for various modes of mass transfer from a zero-temperature helium white dwarf to a neutron star of initially 1.4   M_⊙ with a 12   km radius. The lower dotted curve shows the case of accretion efficiency ϵ = 0 and full feedback (η = 0) (almost all transferred matter lost via isotropic re-emission, hardly any accretion). The middle dotted curve is for ϵ = 1 and η = 0 (conservative mass transfer). The upper dotted curve is for no feedback (η = 1). The zero-temperature white dwarf exponent ζ_d (Sect. 3.3) is represented by the dashed curve. The solid curves starting at q = 0.59 (M_d = 0.83   M_⊙, Sect. 2.3) indicate the actual value of ζ_L (for ϵ shown in Fig. 4) for both the full feedback and no-feedback case. Until q = 0.01 there is full feedback in either case. Below q = 0.01 the full feedback case is shown by the lower solid branch, where the open circle denotes an age of 10 Gyr (since the onset of mass transfer). The no-feedback case has a jump in ζ_L at q = 0.01, after which it follows the upper dotted curve until the intersection with the dashed curve (filled circle) where donor disruption occurs at a system age of 300 Myr.