Solid lines show the CH₃CHO and NH₂CHO abundances (top panel) and their ratio (bottom panel) as predicted by the gas-phase chemistry model that best reproduces our observations in L1157-B. The physical parameter values, as well as the abundances of key reactants injected into the gas phase after the shock passage, are indicated in the upper and bottom panels, respectively. Measurement points in B0, B1, and B2 are shown as crosses whose vertical lengths correspond to the measured abundance and ratio uncertainties (see Table 2), and whose horizontal lengths account for a 500 yr uncertainty in the post-shock time as derived by Podio et al. (2016).