Abstract We propose non-linear equations for the formal Type-B Higher Spin Gravity that is dual to the free fermion or to the product Gross-Neveu model, depending on the boundary conditions.The equations are directly obtained from the first principles: the gauge 9x11 pergola invariance of the CFT partition function on an arbitrary background for single-trace operators.We also get equations describing propagation of certain mixed-symmetry fields over higher spin flat backgrounds.