Magnetic context and flare ribbon evolution of the X9.3 flare in active region NOAA 12673 on 6 September 2017. (a) Two long flare ribbons near the start of the flare are shown in a Ca II 8542 ÅCOCOPLOT. (b) The magnetic context of the flare shows an intrusion of a parasitic, negative-polarity region (left) into the northern portion of the positive-polarity region (right). This image was processed by the convolutional neural network presented in Díaz Baso et al. (2019). Co-temporal (c) Ca II 8542 Åand (d) Hα COCOPLOTs showing the initial expansion of the flare ribbons and the formation of the loop arcade. (e) A sunquake visible in the Ca II 8542 ÅCOCOPLOT occurs before (f) the dramatic further expansion of the flare ribbon to the right of the image.