HashSet<String> LeftHandSide;
                HashSet<String> RightHandSide;
...
                public boolean equals(Object obj) {
                        if(this == obj)
                                return true;
                        if((obj == null) || (obj.getClass() != this.getClass()))
                                return false;
                        // object must be FunctionalDependency at this point
                        FunctionalDependency FD = (FunctionalDependency)obj;
                        return LeftHandSide == FD.LeftHandSide &&
                                RightHandSide == FD.RightHandSide;
                }