gistfile1.java

        Observable<Boolean> passwordObservable = Observable.combineLatest(
                validatePassword(RxViewUtils.text(mPassword)),
                (RxViewUtils.text(mPasswordConfirm)),
                (password, confirm) -> password.equals(confirm));

        Observable.combineLatest(
                validateFirstName(RxViewUtils.text(mUsername)),
                passwordObservable,
                (username, password) -> username && password
        ).subscribe(
                enabled -> {
                    mContinue.setEnabled(enabled);
                }
        );