In prolog, define the prefix predicate so that prefix(x, y) says that x is a list that is a prefix of y. that is, each element of x is equal to (unifies with) the corresponding element of y, but y may contain additional elements after tha. check that your predicate works when x is uninstantiated: given a query like prefix(x, [1,2,3]), it should find all the prefixes of the list [1,2,3].