What are the distinct types of mills that are built by American or Canadian architects?
return architects ;return #1 that  are American ;return #1 that  are Canadian ;return mills built by #2 ;return mills built by #3 ;return #4 ,  #5 ;return the  distinct types of #6
['select', 'filter', 'filter', 'project', 'project', 'union', 'project']