The solution he proposed involved a MR curve that sloped down, then up and then down. His equation for the demand curve (for example) to generate such a MR is $P(q)=1−q+3q^2−3q^3$ (see comments below his answer).
My question is:
Is there an Utility function that can generate a demand curve which gives, say an U-shape looking MR?
Note: I am not looking for an utility function that replicates Ubiquitous's MR.