Before revision:  However, live recommender systems face severe unfairness of exposure with a vocabulary several orders of magnitude larger than that of natural language, implying that (1) MLE will preserve and even exacerbate the exposure bias in the long run in order to faithfully fit the observed samples , and (2) suboptimal sampling and inadequate use of item features can lead to inferior representations for the unfairly ignored items .
After revision:  However, live recommender systems face severe exposure bias and have a vocabulary several orders of magnitude larger than that of natural language, implying that (1) MLE will preserve and even exacerbate the exposure bias in the long run in order to faithfully fit the observed samples , and (2) suboptimal sampling and inadequate use of item features can lead to inferior representations for the unfairly ignored items .