Points with error bars: as Fig. A.1 for HE0024–2523. Solid line: best-fitting model found with model set B and assuming a low efficiency for common-envelope ejection, α_CE = 0.03, which is required to reproduce the observed period of P_orb = 3.14 days in a binary scenario. Dashed line: alternative scenario in which the HE0024–2523 was initially part of a hierarchical triple system. An intermediate-mass primary star was in a wide orbit around a close binary. During its AGB phase the primary star pollutes the inner binary. Subsequently, the secondary star overfills its Roche lobe, the system enters a common envelope the ejection of which (modelled with α_CE = 1.0) requires the orbit to shrink to the observed period.