On the Fradkin-Vasiliev formalism in d = 4

Here we discuss the general properties of the Fradkin-Vasiliev formalism for constructing higher spin cubic interactions. Initially, it was formulated only for massless fields, but later its application was extended to systems of both massless and massive (partially massless) fields. We restrict our discussion to d = 4 , not only for technical reasons (such as the use of multispinor formalism), but mainly because the classification of cubic vertices in d = 4 differs drastically from that in higher dimensions.