Air[]. Foo[contents]. Bar[contents]. Pack[foos, bars]. Organize[a]. Organize[a: Foo[contents]]: Pack[foos: a Pack[ foos: Foo[contents: Bar[contents: Air[]]] | Air[] bars: Bar[contents: Foo[contents: Air[]]] | Air[] ]*/ Organize[ a: Foo[contents: Bar[contents: Air[]]] | Bar[contents: Foo[contents: Air[]]] ]?