The variable _ signifies an anonymous variable; Every instance of _ within a clause is treated being a fresh variable. We enforce the need that every variable in a very clause has to be bound. A variable X is bound if no less than one among the next conditions retains: https://integrated-management-sys55432.wizzardsblog.com/34465132/the-fact-about-integrated-management-system-that-no-one-is-suggesting