Explore the concept of reversal and recirculation in stationary Prandtl equations through this in-depth lecture. Delve into the characteristics of reversal after the Goldstein singularity, examining regions where u > 0 and u < 0. Understand why the classical approach of treating the stationary Prandtl system as an x-evolution equation fails when u changes sign. Learn about the alternative perspective of viewing the problem as a quasilinear, mixed-type, free-boundary problem. Gain insights from the joint work of Nader Masmoudi from New York University and Sameer Iyer, presented at the Institut des Hautes Etudes Scientifiques (IHES) in this hour-long academic talk.