new user error

[HoffHoffyN]

Hi everyone
I am new to GNU prolog
working with SWI-Prolog I was able to define an op such as 
?-op(140, xfy, or).
and then write 
disjunctive(_ or _).
In GNU prolog i get this error:
error: syntax error: , or ) expected (char:14)
what am I doing wrong here?
Alex

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