Prolog Doing a Query

This is directly from a tutorial online, and I get a top down level design error, help?

employee(193,'Jones','John','173 Elm St.','Hoboken','NJ',
                        开发者_Go百科                  12345,1,'25 Jun 93',25500).
employee(181,'Doe','Betty','11 Spring St.','Paterson','NJ',
                                          12354,3,'12 May 91',28500).
employee(198,'Smith','Al','2 Ace Ave.','Paterson','NJ',
                                          12354,3,'12 Sep 93',27000).

Given these basic relations (also called extensional relations), we can define other relations using Prolog procedure definitions to give us answers to questions we might have about the data. For example, we can define a new relation containing the names of all employees making more than $28,000:

well_paid_emp(First,Last) :-
    employee(_Num,Last,First,_Addr,_City,_St,_Zip,_Dept,_Date,Sal),
    Sal > 28000.

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It could be that you are using a Prolog system which shows a singleton warning for well_paid_emp/2.

Not all Prolog systems allow _<Capital><Rest> as singletons, i.e. variables that occur only once in a rule.