From what date and to what date do the staff work on a project that has the most staff and has staff in a leader role?
return projects ;return staff  of #1 ;return number of  #2 for each #1 ;return #1 where #2 has a leader role ;return #4 where #3 is highest ;return date  that #2 work on #5 from  ;return date  that #2 work on #5 to ;return #6 ,  #7
['select', 'project', 'group', 'comparative', 'superlative', 'None', 'None', 'union']