Make a filter can be little complicate.
See:
{"jsonrpc": "2.0", "method": "videoLibrary.Gettvshows", "params": { "sort": {"order": "descending", "method": "lastplayed"},
"filter": {and:["or":[{"field": "inprogress", "operator": "true", "value": ""},{"field": "genre", "operator": "startwith", "value": "a"}],{"field": "title", "operator": "startwith", "value": "a"}}],
"proerties"["title"] }, "id": 1}
First the xbmc will see if the tvshow has a inprogress field or the genre start with "a", if one of this its true the xbmc will see if the title start with the char "a" .