Set Primitive Projections. Class Foo (F : False) := { foo : True }. Arguments foo F {Foo}. Print Implicit foo. (* foo : forall F : False, Foo F -> True Argument Foo is implicit and maximally inserted *) Check foo _. (* Toplevel input, characters 6-11: Error: Illegal application (Non-functional construction): The expression "foo" of type "True" cannot be applied to the term "?36" : "?35" *)