A scientist is studying factors which in?uence the population of lions in a particular jungle. In particular, she is investigating the effect of average temperature, average rainfall, number of related predators and number of prey. She believes that the number of lions should be a smooth function of the 4 predictors, and that the effect of the predictors have little interaction with each other. She would like a ?exible model that allows the effect of each predictor to be very different in different regions of the input values. Propose a reasonable model for this setting.