“…It can even be a little bit of both, as in the first description of the RABBITT scheme in 1990 [175], or in single-photon laser-enabled Auger decay (sp-LEAD), which was predicted in 2013 [176], first observed in 2017 [177], and further characterised in [178]. There are also theoretical predictions-both analytical, like molecular Auger interferometry [179], and numerical, like HHG in topological solids [180][181][182]-which have already sparked experimental efforts to confirm them, but which are still waiting for their observations to come. On the other side, we have discoveries which arise from experimental observations and are then explained theoretically, such as NSDI, which was discussed in detail in Sect.…”