... Actor Prolog supports so-called repeated proving of sub-goals. ... Logical actors are a name of these repeatedly proved sub-goals. ... A logic program consists of sub-goals that must be proven in the course of an execution of the program (like a usual imperative program consists of commands to be executed). ... There are some logical actors in the outside world from the standpoint of the ideology of Actor Prolog , and a program interacts with these external actors. ...