The timeline of a ZLB episode is presented in table 1A. The phase diagram of the NK model comes from figure 1C. The phase diagram of the WUNK model comes from figure 1D. The equilibrium trajectories are the unique trajectories reaching the natural steady state (where $π=0$ and $y=yn$⁠) at time $T$⁠. The figure shows that the economy slumps during the ZLB: inflation is negative, and output is below its natural level (A, B). In the NK model, the initial slump becomes unboundedly severe as the ZLB lasts longer (C). In the WUNK model, there is no such collapse: output and inflation are bounded below by the ZLB steady state (D).