Composition (colored solid lines) and velocity (dashed line) profiles versus Lagrangian mass for the helium-star explosion model he4p0 of Ertl et al. (2020). A boxcar mixing set to 0.06 M_ej has been applied four times. Our ansatz assumes that the material from the helium-star explosion and its pre-explosion mass loss has all been swept-up into a dense shell. The adopted density profile of the dense shell is given by a Gaussian with a center at 2000 km s⁻¹ and a standard deviation of 70 km s⁻¹. The density in such a shell is 100–1000 times greater than in the inner ejecta of the he4p0 model without interaction.