In-out semi-classical gravity and 1N quantum gravity

Classical gravity with higher derivatives, when coupled to the in-out matrix element of T_μν: (a) appears to be free from instabilities of the in-in theory; (b) may be considered as the “underlying classical theory” to Tomboulis' $\text{1}\text{N}\text{-}\text{resummed}$ quantum gravity. I explain how these two facts may be adduced as evidence for the viability both of the former semi-classical approximation and of the latter approach to full quantum gravity.