The advanced search allows one to search with two words. They can either require (1) both terms to be found (and); or (2) either one or the other (or both) of the terms be found (or). It is also possible to have the second term false (not). The (or) and (not) combination is not particularly useful. 

     For instance if term(1)="Dakota" and term(2)="South" and you used the and option, the search would find localities in South Dakota, but would not find any for North Dakota. If you used term(1)="york" and term(2)="Society" and you used the and and not options; the program would find New York localities, but would leave out those articles on the New York Mineralogical Society.