Prediction for the positions of the planets and their Lagrangian points at different epochs. Left: minimum observing date to detect the co-orbital motion in the orbit of planet PDS 70 b. Right: equivalent for the orbit of planet PDS 70 c. Transparent symbols are the position in the current image epoch (July 2019), while solid symbols are for the epoch in the title. Same ALMA continuum image with the same projected orbits as in Fig. 1. Contours are 3, 3.5, 4, and 8-σ.