By concavity of yv(y),18 5 < y*. Innovations are too small under laissez-faire.
This result is another manifestation of the business-stealing effect. The social
planner chooses y so as to maximize the arrival rate multiplied by the net size
(y - 1) of innovations, whereas the private research firm, which does not
internalize the loss of the existing vintage of intermediate good, maximizes the
arrival rate times the gross size y.