how to prevent the second observable to execute?

[jiangecho]

Thanks.

      Observable<Data> source = Observable.concat(
                sources.memory(),
                sources.disk(),
                sources.network()
            )
            .first(data -> data != null && data.isUpToDate());

I want to know when the first()'s condition is true, is there any way to present the following observable to execute?

Thank you.

[jiangecho]

sorry, I found my mistake, I put .compose() before .first(), so ... please close this issue.