“…A closer inspection reveals that most of these solutions lie outside the realm of our analysis, relying on: threshold corrections to the gauge coupling [15,16], worldsheet instantons (discussed above) [10], or a combination of these [9,11], strong coupling effects [17][18][19][20], or other non-perturbative dynamics [21]. However, there appear to be a few puzzling exceptions [22][23][24][25], which are at odds with our findings, since they engineer AdS 4 solutions using a combination of H-flux, α ′ corrections and gaugino condensates. According to our analysis, these solutions should not be possible.…”