Logical operators (AND - OR - NOT ) that make electronic bibliographic reasearch different from the traditional one setbased on a print index. These prepositionsoperators permit to combine different concepts within the same research, in contrast to the traditional research that allows access to contents using only one word at a time. Every preposition has a specific function and leads to a specific result. IN - NEAR - WITH can be also be used as boolean operators.
prepositions: AND, OR are conjunctions, NOT an adverb. This in syntax, but here they are "operators", a collective noun including them all.
Another general remark: the operators were NOT born to serve bibliographic research, so maybe you should explain their history (and also something about how they work)
