I assumed they meant “+” (and that's indeed what's in the paper) which is “split the difference between max customer price and marginal cost”, but that doesn't seem particularly insightful nor worth writing a “research paper” for that… (I'm always baffled how low the bar is for submission in econ journals).
B basically any economic reasoning around “demand curve” and “marginal cost” is meaningless in real world situations.
Demand curve is meaningless because humans don't have a stable and rational assessment of the price they would accept to pay for something (that's why having pretty hostess and expensive packaging are a thing) and this price also depends on many contextual factors: you're OK to pay much for for a glass of Coke in a fancy restaurant that you would accept at Mc Donalds, and a business values a piece of B2B software very differently depending on at which point we are in the fiscal year.
The so-called demand curve is as useful for a business as a population-wide heartbeat distribution would be. It makes no sense to talk about “the” curve, since it changes all the time!
B basically any economic reasoning around “demand curve” and “marginal cost” is meaningless in real world situations.