That looks like ooks like "original research". It's obvious that what is described as dynamic-only duck typing could be statically checked. So that is to say, a given expression foo.bar in the program could be statically checked to make sure that all possible values that foo takes on have property bar. If three classes A, B, C in the program have property foo, then this means verifying that foo is A | B | C. Thus, "static duck typing".