“…Compared to earlier holography proposals [19,20,21], in which the bulk side is a (string) field theory containing higher spin gravity of Vasiliev type [22,23], the proposal of [17] was based on the observation that tensionless strings in anti-de Sitter spacetime behave as collections of conformal particles, that is, on a first-quantized description of the bulk physics. Subsequent tests at the level of on-shell amplitudes in AdS 4 , have shown that traces of Gaussian density matrices of the the quantum mechanical harmonic oscillator in two dimensions describing unfolded boundary-tobulk propagators of massless fields [24], which one may think of as vertex operators on conformal particle worldlines in phase space 4 , or, boundary vertex operators on the corresponding topological open string, indeed reproduce the correlation functions for bilinear operators in free conformal field theories in three dimensions [25,26,27,28] 5 . The current, slightly refined, working hypothesis is that there exists a variant of Witten's realization of Chern-Simons theory as a topological A model [29] (see also [30]), whereby a gauging of the differential Poisson sigma model with 3-graded Chan-Paton factors [31] (see also [32,33]) yields the Frobenius-Chern-Simons formulation [34,35] of higher spin gravity.…”