L1157 southern blueshifted lobe in CO (1–0) (white contours; Gueth et al. 1996) and NH₂ CHO (4_1,4 –3_1,3) (cyan contours; Codella et al. 2017). The precessing jet ejected by the central object L1157-mm (outside the frame and toward the northwest) excavated several clumpy cavities, named B0, B1, and B2, respectively. The maps are centred at α(J 2000) = 20^h 39^m10^s.2, δ(J 2000) = +68°01′10′′.5 (Δα = +25′′ and Δδ = –63′′.5 from the L1157-mm protostar). Map (in colour scale) of the sum of the CH₃ OH (2_-1,2 –1_-1,1) E, (2_0,2 –1_0,1) A, and (2_0,2–1_0,1) E emission lines (labelled 2_k,k–1_k,k), (2_1,2 –1_1,1) A, (2_1,1–1_1,0) A, and (2_1,1–1_1,0) E (integrated over the whole velocity range). For the CO image, the first contour and step are 6σ (1σ = 0.5 Jy beam⁻¹ km s⁻¹) and 4σ, respectively. The first contour and step of the NH₂CHO map (cyan contours) correspond to 3σ (15 mJy beam⁻¹ km s⁻¹) and 1σ, respectively. The dashed circle shows the primary beam of the CH₃OH images (64′′). The first contour and step are 3σ (56, 32, 45, and 23 mJy beam⁻¹ km s⁻¹ for 2_k,k –1_k,k, 2_1,2 –1_1,1 A, 2_1,1 –1_1,0 A, and (2_1,1–1_1,0) E, respectively. Yellow labels are for the B0, B1, and B2 regions: the positions of the different clumps inside these regions are shown in Fig. 1 (see also text, and e.g. Codella et al. 2009, 2017). The cyan, white, and magenta ellipses depict the synthesised beams of the NH₂ CHO (5′′.79 × 4′′.81, PA = –94°), CO (3′′.65 × 2′′.96, PA = +88°), and CH₃OH (2′′.97 × 2′′.26, PA = –155°) observations, respectively.