tuple variable造句

For the construction of the formulas we will assume an infinite set " V " of tuple variables.
An interesting property of these queries is that if we assume that the tuple variables range over tuples over the so-called " active domain " of the database, which is the subset of the domain that occurs in at least one tuple in the database or in the query expression, then the semantics of the query expressions does not change.
It's difficult to find tuple variable in a sentence. 用tuple variable造句挺难的