Prolog; a question about notation in an assignment

I get hat isa开发者_Python百科/2 is a rule, that takes two objects or terms. But what would isa2/2 imply? That isa is defined twice?

isa2/2 simply refers to a predicate named isa2 taking 2 arguments, i.e. the first 2 is simply part of the name, not a special notation.