Knot identification in the SOUL H2 continuum-subtracted image of the IRAS 20126-4104 flow and knot proper motions. Panel a: zoom-in on the A and X knot regions (red-shifted lobe). Contour levels at 5, 7, 10, 15, 20, and 25σ are overlaid. We note that 1σ corresponds to 8×10⁻²³ W cm⁻² arcsec⁻². Panel b: zoom-in on the B and C1 knot regions (blue-shifted lobe). Contour levels at 5, 7, 10, 15, 30, and 40σ are overlaid. Panel c: zoom-in on the C1 and C2 knot regions (blue-shifted lobe). Contour levels at 5, 10, 20, 30, 40, 50, 60, 80, and 120σ are overlaid. Knot peaks are indicated by white dots. Panel d: overall view of the IRAS 20126+4104 flow close to the source. The main structures as reported in Caratti o Garatti et al. (2008) are labelled. Panel e: proper motions (PMs) with their uncertainties (blue arrows and red ellipses) in 100 yr of structures and sub-structures along the H₂ jet in IRAS20126+4104. The actual observed shifts are approximately one fourth the length of the corresponding arrow. The red circle marks the position (along with its uncertainty) of the protostellar continuum emission at 1.4 mm (Cesaroni et al. 2014). The main structures as labelled in Caratti o Garatti et al. (2008) are also indicated.