The multi-fold theory factually encounters the AdS/CFT correspondence conjecture. On the other hand, the conventional AdS/CFT conjecture can also be understood as a mathematical duality, where the CFT spacetime is not necessarily physically tangent to AdS(5) (+u2026). It can be justified as a particular case of the holographic principle. Therefore, the paper revisits, and derives the holographic principle, in a multi-fold universe. As General relativity (GR) encounters multi-folds at Planck scales, the proof applies to GR-based universes. We also debunk the use of Wheeler’s bag of gold as a counter example to the holographic principle.Trying to resolve the black hole information paradox, different teams have been able to recover the black hole Page curve, by relying on the replica trick with generalized semi-classical gravitational path integrals, in asymptotic AdS, with arbitrary topologies, including spacetime (Euclidian) wormholes in between replicas, to justifies paths in between the replicas. The approach also relies on the island formula for the von Neuman entropy as fine-grained entropy. One knows that the Page curve had to be recovered one way or another as with the AdS/CFT correspondence conjecture, the unitarity of CFTs implies unitarity of gravity. The quantum extremal surface that appears in the process, bounding the island, leads to proposed physical interpretations of a black hole interior, that, in our opinion creates confusions than answers. In the multi-fold theory, we have already encountered an equivalent surface, with a much cleaner microscopic interpretation. The paper discusses the differences between the two interpretations. A few recent papers reused the approach to study two entangled gravitating universes, with one possibly without gravity. This paper provides multi-fold inspired interpretations of the quantum extremal surfaces appearing among the disjoint universes.Interpreting the replica trick, and its wormholes, one can see that the role played by the wormholes between different replicas amounts to the multi-fold mechanisms.. This is further reinforced by considerations on global symmetry in the presence of gravity or wormholes. The islands associated to the different entangled universe use cases also imply that, in universes with gravity, entanglement implies gravity effects, which is also known as the E/G conjecture. It means that the M-theory encounters multi-folds. The multi-fold theory could have predicted such an outcome from the link between the Hilbert Einstein action and superstring action, and the fact that we already had GR encounter multi-folds at Planck scales.