Static type checking without downcast operator

In the last couple of years several dynamically-typed, object-oriented programming languages have been equipped with optional static type checkers. This typically requires these to be extended a downcast operator, which is common operator in statically-typed but not dynamically-typed languages. Our objective investigate an approach for checking that does require such additional operator. We systematically weaken rules avoid reporting errors can resolved using operators. leads similar quasi-static typing enables make annotations stricter gradual way. These applied by interpreting dynamic as top subtype relation. Based on ideas we implemented checker language POOSL without introducing Practical experiences this indicate it useful early validation.