[eclipse-users] Newbie: not consecutive procedure clauses

Hello,

whenever I compile the following code from the book "Learn Prolog Now!",

wizard(ron).
hasWand(harry).
wizard(X):- hasBroom(X), hasWand(X).
quidditchPlayer(harry).
hasBroom(X) :- quidditchPlayer(X).

I get the following message,

*** procedure clauses are not consecutive: wizard / 1
         before line 6 in the file /Applications/eclipse/myscripts/ 
harry.pl
harry.pl   compiled traceable 116 bytes in 0.00 seconds

Yes (0.00s cpu)

Could someone please explain why my procedure clauses should be  
"consecutive"?

Many thanks.

Best regards,

Philippe