sentences:  He gives PSL(2,11) and the alternating group of degree 5 as examples, and of course every alternating group of prime degree is an example.This same paper gives a number of examples of groups which cannot be realized as Zappa–Szép products of proper subgroups, such as the quaternion group and the alternating group of degree 6.As with the direct and semidirect products, there is an external version of the Zappa–Szép product for groups which are not known "a priori" to be subgroups of a given group.