More than this; he wrote to divorce his wife, etc. - יתר מיכן כתב לגרש את אשתו כולי
Summary:
The יתר מיכן can be understood that the first case can be derived from the second case, or as long as there is some חידוש in the second case we can say יתר מיכן. The משנה of הכותב טופסי גיטין was written to teach us a leniency.