You then can call the functions using standard function call syntax, by combining this prefix with the name of the method to be invoked.

Just as iterators are a generalization of Pointers, function objects are a generalization of functions: a function object is anything that you can call using the ordinary function call syntax.

Think of this as a function that takes two techs arguments, the first of which is univs and the second of which is techs. And this is just a different syntax for writing that function call.