“…The main ingredients of our proof are two difference equations. One of these is obtained from a certain functional representation of the AL hierarchy due to Vekslerchik [32, 33], while the other was proved by one of us in [3] by adapting ideas which appeared in the study of the exact Wentzel–Kramers–Brillouin (WKB) method in [25]. In particular, by combining this with the results of Bridgeland in [8], we are able to obtain a closed‐form expression for the tau function, thus providing a new, but perhaps expected, link between integrable hierarchies of GW theory and Bridgeland's DT Riemann–Hilbert problem.…”